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Investigating the interrelationship between rated L2 proficiency and linguistic complexity in L2 speech

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This study investigates the relationship between nine quantitative measures of L2 speech complexity and subjectively rated L2 proficiency by comparing the oral productions of English L2 learners at five IELTS proficiency levels. We carry out ANOVAs with pairwise comparisons to identify between which proficiency levels the observed differences are to be situated, as well as ordinal logistic regression modelling, allowing us to combine multiple complexity dimensions in a single analysis. The results show that for eight out of nine measures, targeting syntactic, lexical and morphological complexity, a significant overall effect of proficiency level was found, with measures of lexical diversity (i.e. Guiraud's index and HD-D), overall syntactic complexity (mean length of AS-unit), phrasal elaboration (mean length of noun phrase) and morphological richness (morphological complexity index) showing the strongest association with proficiency level. Three complexity measures emerged as significant predictors in our logistic regression model, each targeting different linguistic dimensions: Guiraud's index, the subordination ratio and the morphological complexity index.
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Contents lists available at ScienceDirect
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1. Introduction
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2. Literature review
2.1. L2 complexity
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2.2. Operationalising L2 pro>ciency
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?J=9LDQ 9;JGKK ) KLM<A=K ,JL=?9  1@GE9K  1@AK AK 9DKG L@= ;9K= >GJ KLM<A=K L@9L @9N= AFN=KLA?9L=< L@= DAF?MAKLA; >=9LMJ=K
L@9L ;GJJ=D9L= OAL@ GJ <AKLAF?MAK@ :=LO==F ) HJG\;A=F;Q D=N=DK  FME:=J G> KLM<A=K @9N= L9C=F KLM<=FLK;GMJK= D=N=D 9K 9 E=9KMJ= G>
L@=AJ HJG\;A=F;Q =? )M  O@AD= GL@=JK MK= @GDAKLA; J9LAF? K;9D=K =AL@=J <=KA?F=< :Q J=K=9J;@=JK  GFFGJ)AFLGF -GDAG 
GJ MK=< AF KL9F<9J<AK=< D9F?M9?= L=KLK KM;@ 9K 1,"#) &O9K@AL9 JGOF *;+9E9J9  ,%9?9F  GJ &")10 /=9<  +9LAGF 
0==<@GMK= %9JJAK +9=: SKLYF=D  FME:=J G> KLM<A=K @9N= 9DKG GH=J9LAGF9DAK=< HJG\;A=F;Q AF L=JEK G> "#/ D=N=DK ::9K
(@MK@AC  %M@L9  $QDDKL9< =L 9D  &F 9 E=L99F9DQKAK G> ) OJALAF? KLM<A=K ,JL=?9  G:K=JN=< L@9L HJG\;A=F;Q D=N=DK
:9K=< GF @GDAKLA; J9LAF? QA=D<=< EGJ= @GEG?=F=GMK K9EHD=K L@9F L@GK= :9K=< GF HJG?J9EE= D=N=D
2.3. L2 speech complexity and L2 pro>ciency
 ;GFKA<=J9:D= FME:=J G> KLM<A=K AFN=KLA?9L=< L@= J=D9LAGFK@AH :=LO==F ) HJG\;A=F;Q 9F< ) OJALAF? ;GEHD=PALQ :ML >GJ L@= HMJ
HGK= G> GMJ KLM<Q O= 9J= E9AFDQ AFL=J=KL=< AF KLM<A=K L9J?=LAF? ) KH==;@ "N=F L@GM?@ KGE= KLM<A=K @9N= AFN=KLA?9L=< ;GEHD=PALQ
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246
AF D9F?M9?=K GL@=J L@9F "F?DAK@ KM;@ 9K ) '9H9F=K= &O9K@AL9  ) $=JE9F +=9JQ0MF<IMAKL  9F< ) #J=F;@ != D=J;I
 != D=J;I %GMK=F   L@= >G;MK AF L@AK KLM<Q AK GF ) "F?DAK@ 9K @9K :==F L@= ;9K= >GJ EGKL KLM<A=K KG >9J 19:D=
 HJGNA<=K 9F GN=JNA=O G> FAF= KLM<A=K L@9L @9N= AFN=KLA?9L=< L@= J=D9LAGFK@AH :=LO==F ;GEHD=PALQ 9F< GJ9D HJG\;A=F;Q >GJ "F?DAK@
9K 9 K=;GF< GJ >GJ=A?F D9F?M9?= AF<A;9LAF? L@= FME:=J G> H9JLA;AH9FLK H=J KLM<Q 9K O=DD 9K L@= FME:=J 9F< J9F?= G> HJG\;A=F;Q D=N
=DK 9F< L@= O9Q AF O@A;@ HJG\;A=F;Q 9F< ;GEHD=PALQ 9J= GH=J9LAGF9DAK=<K ;9F := K==F AF 19:D=  L@= \JKL L@J== KLM<A=K >G;MK=<
=P;DMKAN=DQ GF D=PA;9D ;GEHD=PALQ L@J== KLM<A=K AFN=KLA?9L=< KQFL9;LA; ;GEHD=PALQ LOG KLM<A=K AF;DM<=< E=9KMJ=K G> :GL@ D=PA;9D 9F<
KQFL9;LA; ;GEHD=PALQ 9F< GFDQ GF= KLM<Q DGGC=< 9L EGJH@GDG?A;9D ;GEHD=PALQ
1@= \JKL 9JLA;D= 9<<J=KKAF? L@= J=D9LAGFK@AH :=LO==F GJ9D HJG\;A=F;Q 9F< D=PA;9D ;GEHD=PALQ J=HGJLK GF 9 ;GEH9JAKGF :=LO==F "F?
DAK@ 9F< #J=F;@ 9K 9 >GJ=A?F D9F?M9?= AF KHGC=F <9L9 ?9L@=J=< >JGE  K=;GF<9JQ K;@GGD D=9JF=JK OAL@ ) !ML;@ != D=J;I 
1@= L=PLK O=J= <ANA<=< AFLG >GMJ HJG\;A=F;Q D=N=DK :9K=< GF L@= D=9JF=JK 9?= 9F< L@=AJ D=N=D G> DAF?MAKLA; 9;;MJ9;Q AF L@= ) != D=J;I
 KLM<A=< L@= <=N=DGHE=FL G> D=PA;9D ;GEHD=PALQ AF L@=K= >GMJ D=N=DK 9F< @= ;GF;DM<=< L@9L L@= E=9KMJ=K G> D=PA;9D <AN=JKALQ !
$MAJ9M<K AF<=P O=J= :=KL 9:D= LG <AKLAF?MAK@ :=LO==F HJG\;A=F;Q D=N=DK GL@ ! 9F< $MAJ9M<K AF<=P O=J= 9:D= LG <A>>=J=FLA9L= :=
LO==F 9<B9;=FL D=N=DK  9F<  9F<  9F<  :ML FG <A>>=J=F;=K O=J= >GMF< :=LO==F D=N=DK  9F<  A= L@= LOG @A?@=KL D=N=DK
)M  9F9DQK=< L@J== LQH=K G> D=PA;9D ;GEHD=PALQ MKAF? 9 OA<= J9F?= G> E=9KMJ=K >GJ =9;@ AF  GJ9D F9JJ9LAN=K H=J>GJE=< :Q
@AF=K= ;GDD=?=D=N=D D=9JF=JK G> "F?DAK@ O@G O=J= J9L=< GF 9 @GDAKLA; JM:JA; 9F< ?JGMH=< AFLG >GMJ HJG\;A=F;Q D=N=DK 1@= 9ML@GJ MK=<
;GEHML=J:9K=< 9F9DQK=K LG ;9D;MD9L= E=9KMJ=K G> D=PA;9D <=FKALQ D=PA;9D KGH@AKLA;9LAGF 9F< D=PA;9D N9JA9LAGF ,FDQ D=PA;9D N9JA9LAGF
9HH=9J=< LG := 9 ?GG< HJ=<A;LGJ G> HJG\;A=F;Q O@A;@ AK AF DAF= OAL@ != D=J;IK  \F<AF?K "N=F L@GM?@ )M  H=J>GJE=<
+,3K LG AFN=KLA?9L= O@=L@=J E=9KMJ=K QA=D<=< KA?FA>A;9FL <A>>=J=F;=K :=LO==F D=N=DK L@= 9ML@GJ <A< FGL ;9JJQ GML HGKL@G; 9F9DQK=K
LG \F< GML O@=J= L@= <A>>=J=F;=K O=J= DG;9L=<
,> L@= LOG KLM<A=K L@9L DGGC=< 9L ;GEHD=PALQ 9F< GJ9D HJG\;A=F;Q MKAF? <9L9 >JGE L@= &")10 KH=9CAF? L=KL GF= >G;MK=< GF D=PA;9D
;GEHD=PALQ /=9< 9F< +9LAGF  ;9D;MD9L=< L@= GN=J9DD FME:=J G> LGC=FK 9F< LQH=K D=PA;9D N9JA9LAGF ! 9F< D=PA;9D KGH@AKLA;9LAGF
D9E:<9 >GJ  K9EHD=K J9F?AF? >JGE :9F<  LG :9F<  &F ?=F=J9D L@= FME:=J G> OGJ<K HJG<M;=< D=PA;9D N9JA9LAGF 9F< L@= FME:=J
G> AF>J=IM=FL GJ KGH@AKLA;9L=< OGJ<K AF;J=9K=< ?J9<M9DDQ >JGE :9F<K  LG  :ML L@=J= O9K 9 DGL G> N9JA9LAGF OAL@AF =9;@ D=N=D 9F<
L@= 9ML@GJK <A< FGL H=J>GJE KL9LAKLA;9D L=KLK LG 9K;=JL9AF A> L@=K= <A>>=J=F;=K O=J= KA?FA>A;9FL GJ @GO O=DD L@= ;@GK=F E=9KMJ=K ;GMD<
<AKLAF?MAK@ :=LO==F D=N=DK
4AL@ J=?9J< LG KQFL9;LA; ;GEHD=PALQ != D=J;I 9F< %GMK=F  9F9DQK=< L@= K9E= <9L9K=L 9K != D=J;I  9F< >GMF< L@9L
D=F?L@ G> 0MFAL 9F< ;D9MK=K H=J 0MFAL O=J= L@= E=9KMJ=K L@9L EGKL ;D=9JDQ <AKLAF?MAK@=< :=LO==F HJG\;A=F;Q D=N=DK O@AD= LOG G>
L@= <AN=JKALQ E=9KMJ=K 9DKG QA=D<=< KA?FA>A;9FL <A>>=J=F;=K :=LO==F D=N=DK A= 0MFAL <AN=JKALQ 9F< 0QFL9;LA; !AN=JKALQ &F<=P
$9F  9DKG 9F9DQK=< \N= E=9KMJ=K G> KQFL9;LA; ;GEHD=PALQ AF LOG <A>>=J=FL GJ9D =P9E L9KCK L@9L O=J= H9JL G> 9 F9LAGF9D "F?DAK@
L=KL AF %GF? (GF? 0LM<=FLK @9< LG H=J>GJE 9 EGFGDG?M= 9F< 9 ?JGMH <AK;MKKAGF O@A;@ O=J= J9L=< :Q L@=AJ L=9;@=J :9K=< GF 9F9DQLA;9D
K;9D=K J=KMDLAF? AF KAP HJG\;A=F;Q D=N=DK 1@= GFDQ E=9KMJ= L@9L ;GJJ=D9L=< KA?FA>A;9FLDQ OAL@ L@= ?DG:9D L=KL K;GJ=K O9K E=9F D=F?L@ G>
MLL=J9F;=
1@= GFDQ KLM<Q LG L@= :=KL G> GMJ CFGOD=<?= O@A;@ @9K AFN=KLA?9L=< KQFL9;LA; ;GEHD=PALQ 9L <A>>=J=FL D=N=DK G> L@= &")10 KH=9CAF?
L=KL AK 0==<@GMK= =L 9D  1@=K= 9ML@GJK GFDQ MK=< LOG E=9KMJ=K G> KQFL9;LA; ;GEHD=PALQ :GL@ L9J?=LAF? ;D9MK=DAFCAF? :Q E=9FK
G> KM:GJ<AF9LAGF MFALK H=J 0MFAL 9F< MFALK H=J LGL9D FME:=J G> OGJ<K #GKL=J 1GFCQF 9F< 4A??D=KOGJL@  H <=\F=
MFALK 9K KM:GJ<AF9L= ;D9MK=K O@A;@ @9N= 9L D=9KL 9 \FAL= GJ FGF\FAL= N=J: =D=E=FL HDMK 9L D=9KL GF= GL@=J ;D9MK= =D=E=FL KM;@ 9K
KM:B=;L G:B=;L ;GEHD=E=FL GJ 9<N=J:A9D GL@ E=9KMJ=K ?9N= JAK= LG KL9LAKLA;9DDQ KA?FA>A;9FL <A>>=J=F;=K :=LO==F :9F<K :ML FG AF>GJ
E9LAGF AK AF;DM<=< 9:GML O@=J= L@= <A>>=J=F;=K 9J= DG;9L=<
&O9K@AL9 =L 9D  KLM<A=< 9 FME:=J G> E=9KMJ=K G> 9;;MJ9;Q ]M=F;Q 9F< ;GEHD=PALQ AF \N= <A>>=J=FL D=N=DK G> L@= 1,"#)
A1 KH=9CAF? L=KL 1@= ;GEHD=PALQ E=LJA;K O=J= E9AFDQ KQFL9;LA; E=9KMJ=K =N=F L@GM?@ GF= E=9KMJ= G> D=PA;9D ;GEHD=PALQ O9K 9DKG
AF;DM<=< #GJ KQFL9;LA; ;GEHD=PALQ KA?FA>A;9FL <A>>=J=F;=K :=LO==F D=N=DK O=J= GFDQ G:K=JN=< >GJ N=J: H@J9K=K H=J 1MFAL 9F< E=9F
D=F?L@ G> MLL=J9F;= 4AL@ J=?9J< LG D=PA;9D ;GEHD=PALQ L@= FME:=J G> LQH=K 9F< LGC=FK KA?FA>A;9FLDQ AF;J=9K=< >JGE D=N=D  LG D=N=D
 %GO=N=J FG AF>GJE9LAGF AK HJGNA<=< 9:GML O@=J= =P9;LDQ L@= <A>>=J=F;=K DA= 9F< O@=L@=J GJ FGL L@=K= E=9KMJ=K ;9F <AK;JAEAF9L=
:=LO==F 9<B9;=FL D=N=DK
(9F?  AFN=KLA?9L=< O@A;@ >=9LMJ=K ;GMD< <AKLAF?MAK@ :=LO==F <A>>=J=FL D=N=DK G> L@= 9E:JA<?= "F?DAK@ KH=9CAF? L=KLK  LG
 >G;MKAF? GF ]M=F;Q HJGFMF;A9LAGF 9F< ?J9EE9LA;9D 9F< D=PA;9D ;GEHD=PALQ #GJ D=PA;9D ;GEHD=PALQ KA?FA>A;9FL <A>>=J=F;=K :=
LO==F D=N=DK O=J= >GMF< >GJ L@= LQH=LGC=F J9LAG =N=F L@GM?@ L@= AF;J=9K= O9K FGL DAF=9J >JGE L@= DGO=KL LG L@= @A?@=KL D=N=D #GJ
L@= D=PA;9D E=9KMJ=K <A>>=J=F;=K O=J= E9AFDQ DG;9L=< :=LO==F  9F<  9F< :=LO==F 9F<  :ML FGL :=LO==F  9F<  DD
E=9KMJ=K G> KQFL9;LA; ;GEHD=PALQ MF<=J AFN=KLA?9LAGF =P;=HL L@= FME:=J G> 1MFALK ?9N= JAK= LG KA?FA>A;9FL <A>>=J=F;=K OAL@ KQFL9;LA;
;GEHD=PALQ AF;J=9KAF? >JGE L@=  LG L@= D=N=D *GJ=GN=J LGL9D FME:=J G> ;D9MK=K LGL9D FME:=J G> <=H=F<=FL ;D9MK=K 9F< ;D9MK=K
H=J 1MFAL O=J= >GMF< LG <AKLAF?MAK@ :=LO==F   9F< 
#AF9DDQ O= GFDQ >GMF< GF= KLM<Q L@9L AFN=KLA?9L=< L@= J=D9LAGFK@AH :=LO==F EGJH@GDG?A;9D ;GEHD=PALQ 9F< GJ9D HJG\;A=F;Q !=
D=J;I 9F< %GMK=F  O@G 9F9DQK=< L@J== E=9KMJ=K G> EGJH@GDG?A;9D ;GEHD=PALQ AF L@= K9E= GJ9D F9JJ9LAN=K L@9L O=J= MK=< :Q
!= D=J;I  9F< != D=J;I 9F< %GMK=F  1@= E=9KMJ=K 9F9DQK=< O=J= LQH=K H=J >9EADQ %GJKL GDDAFK 
1@= KLM<A=K :Q != D=J;I  9F< != D=J;I 9F< %GMK=F   ;GEH9J= ;GEHD=PALQ AF "F?DAK@ 9F< #J=F;@ EGFGDG?M=K H=J>GJE=< :Q L@= K9E= D=9JF=JK
:ML >GJ L@= HJ=K=FL KLM<Q O= E9AFDQ >G;MK GF L@= J=KMDLK >GJ "F?DAK@
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246
Table 1
(=Q ;@9J9;L=JAKLA;K G> FAF= KLM<A=K AFN=KLA?9LAF? L@= J=D9LAGFK@AH :=LO==F ) KH==;@ ;GEHD=PALQ 9F< ) HJG\;A=F;Q
0LM<Q )=9JF=JK
+ME:=JG>
HJG\;A=F;QD=N=DK /9F?=G>HJG\;A=F;QD=N=DK -JG\;A=F;Q9KK=KKE=FL GEHD=PALQE=9KMJ=K
!= D=J;I  =?AFF=J9<N9F;=< ?=9F<9;;MJ9;Q )=PA;9DN9JA9LAGF!
$MAJ9M<KAF<=P>GJFGMFK
9F<N=J:K
4GJ<>J=IM=F;Q9F<J=9;
LAGFLAE=
)=P=EA;<=FKALQ
GDDG;9LAGF9D<=FKALQ
)M   $=F=J9DD9:=DKGFDQ>9ADH9KK
?GG<=P;=DD=FL
%GDAKLA;JM:JA; )=PA;9D<=FKALQ
D=PA;9DKGH@AKLA;9LAGF
E=9KMJ=K
D=PA;9DN9JA9LAGFE=9
KMJ=K
/=9<9F<+9LAGF
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 9F<LG:9F< &")10 LGC=FK
LQH=K
)=PA;9DN9JA9LAGF!
)=PA;9DKGH@AKLA;9LAGF
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%GMK=F
 =?AFF=J9<N9F;=< ?=9F<9;;MJ9;Q *=9FD=F?L@G>FGMF
H@J9K=;D9MK=0MFAL
D9MK=KH=J0MFAL
0QFL9;LA;<AN=JKALQ
$9F   +GAF>GJE9LAGF %GF?(GF?F9LAGF9D
"F?DAK@L=KLK;GJ=K
*=9FD=F?L@G>1MFAL
D9MK=KH=J1MFAL
!=H=F<=FL;D9MK=KH=J
;D9MK=
3=J:H@J9K=KH=J1MFAL
*=9FD=F?L@G>MLL=J9F;=
0==<@GMK==L9D

 9F<LG:9F< &")10 MFALKH=J0MFAL
MFALKH=JLGL9DFME:=J
G>OGJ<K
&O9K@AL9=L9D

 +GAF>GJE9LAGF 1,"#)A1K;GJ=K D9MK=KH=J1MFAL
!=H=F<=FL;D9MK=KH=J
;D9MK=
3=J:H@J9K=KH=J1MFAL
*=9FD=F?L@G>MLL=J9F;=
LGC=FK
LQH=K
Table 1 Continued
0LM<Q )=9JF=JK
+ME:=JG>
HJG\;A=F;QD=N=DK /9F?=G>HJG\;A=F;QD=N=DK -JG\;A=F;Q9KK=KKE=FL GEHD=PALQE=9KMJ=K
(9F?  LG  9E:JA<?="F?DAK@ 1QH=LGC=FJ9LAG
)=PA;9D<=FKALQ
)=PA;9DKGH@AKLA;9LAGF
1MFALK;D9MK=K<=H=F
<=FL;D9MK=K
D9MK=KH=J1MFAL
!= D=J;I9F<
%GMK=F
 =?AFF=J9<N9F;=< ?=9F<9;;MJ9;Q 1QH=KH=J>9EADQ
&F]=;LAGF9D<AN=JKALQ
*GJH@GDG?A;9D;GEHD=PALQ
AF<=P
*9DN=JF @AH=J= /A;@9J<K 9F< !MJTFK  &F]=;LAGF9D !AN=JKALQ 9F< -9DDGLLAK  *GJH@GDG?A;9D GEHD=PALQ &F<=P #GJ L@=
"F?DAK@ <9L9 L@=K= E=9KMJ=K ;GMD< GFDQ <AK;JAEAF9L= :=LO==F L@= DGO=KL D=N=D GF L@= GF= @9F< 9F< L@= L@J== @A?@=KL D=N=DK GF L@=
GL@=J
&F ;GF;DMKAGF L@= KLM<A=K G> L@= J=D9LAGFK@AH :=LO==F ) HJG\;A=F;Q 9F< ) KH=9CAF? ;GEHD=PALQ J=NA=O=< @=J= HJGNA<= 9 JA;@
9F< N9JA=< HA;LMJ= L@9L AK FGL =9KADQ KMEE9JAK=< <M= LG <A>>=J=F;=K AF J=K=9J;@ <=KA?F J=D9LAF? LG L@= GH=J9LAGF9DAK9LAGF G> :GL@ ;GE
HD=PALQ 9F< HJG\;A=F;Q L@= K9EHD= G> ) D=9JF=JK 9F9DQK=< 9F< L@= KL9LAKLA;9D 9F9DQK=K &F KHAL= G> L@=K= E=L@G<GDG?A;9D <A>>=J=F;=K
9 FME:=J G> LJ=F<K ;9F := <AKLADD=< >JGE L@= KLM<A=K <AK;MKK=< 9:GN= 4AL@ J=?9J< LG D=PA;9D ;GEHD=PALQ E=9KMJ=K G> D=PA;9D <AN=JKALQ
$MAJ9M<K AF<=P 9F< ! AF H9JLA;MD9J 9HH=9J LG := :=KL 9:D= LG <AKLAF?MAK@ :=LO==F HJG\;A=F;Q D=N=DK 9F< HGL=FLA9DDQ 9DKG :=LO==F
9<B9;=FL D=N=DK L L@= D=N=D G> KQFL9;LA; ;GEHD=PALQ =KH=;A9DDQ L@GK= E=9KMJ=K L9J?=LAF? L@= 9N=J9?= D=F?L@ G> KMHJ9;D9MK9D MFALK A=
1MFALK 0MFALK GJ MLL=J9F;=K 9F< L@GK= L9HHAF? AFLG ;D9MK9D KM:GJ<AF9LAGF =? ;D9MK=K H=J 0MFAL GJ 1MFAL @9N= :==F K@GOF LG
AF;J=9K= OAL@ AF;J=9KAF? HJG\;A=F;Q 1@= GFDQ =NA<=F;= J=?9J<AF? EGJH@GDG?A;9D ;GEHD=PALQ K==EK LG KM??=KL L@9L E=9KMJ=K L9J?=LAF?
L@AK 9KH=;L G> ;GEHD=PALQ 9J= GFDQ 9:D= LG <AKLAF?MAK@ :=LO==F D=9JF=JK 9L DGO HJG\;A=F;Q D=N=DK AF ) "F?DAK@
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246
3. Research questions
"N=F L@GM?@ 9 FME:=J G> KLM<A=K @9N= AFN=KLA?9L=< L@= J=D9LAGFK@AH :=LO==F ;GEHD=PALQ 9F< GJ9D HJG\;A=F;Q AF ) "F?DAK@ O= @9N=
K==F L@9L EGKL G> L@=K= KLM<A=K L=F< LG >G;MK =AL@=J GF D=PA;9D ;GEHD=PALQ GJ KQFL9;LA; ;GEHD=PALQ 9F< GFDQ GF= KLM<Q @9K AFN=KLA?9L=<
EGJH@GDG?A;9D ;GEHD=PALQ #=O KLM<A=K @9N= 9DKG HJGNA<=< AF>GJE9LAGF 9:GML O@A;@ E=9KMJ=K <AKLAF?MAK@ :=LO==F O@A;@ HJG\;A=F;Q
D=N=DK GJ O@A;@ ;GE:AF9LAGF G> E=9KMJ=K :=KL HJ=<A;LK HJG\;A=F;Q 1@= HJ=K=FL KLM<Q K==CK LG 9<<J=KK L@AK ?9H :Q 9F9DQKAF? 9 J9F?=
G> KQFL9;LA; D=PA;9D 9F< EGJH@GDG?A;9D ;GEHD=PALQ E=9KMJ=K 9L \N= <A>>=J=FL HJG\;A=F;Q D=N=DK AFN=KLA?9LAF? O@A;@ E=9KMJ=K :=KL <AK
;JAEAF9L= :=LO==F HJG\;A=F;Q D=N=DK 9F< O@A;@ ;GE:AF9LAGF G> KQFL9;LA; D=PA;9D 9F< EGJH@GDG?A;9D E=9KMJ=K ;9F := MK=< LG HJ=<A;L
HJG\;A=F;Q D=N=D
1@MK L@= HJ=K=FL KLM<Q 9<<J=KK=K L@= >GDDGOAF? :JG9< J=K=9J;@ IM=KLAGFK
 9F E=9KMJ=K G> D=PA;9D KQFL9;LA; 9F< EGJH@GDG?A;9D ;GEHD=PALQ 9HHDA=< LG GJ9D ) "F?DAK@ HJG<M;LAGFK <AK;JAEAF9L= :=LO==F D=9JF
=JK 9L <A>>=J=FL ) HJG\;A=F;Q D=N=DK
9 4@A;@ E=9KMJ=K 9J= :=KL 9:D= LG <AK;JAEAF9L= :=LO==F HJG\;A=F;Q D=N=DK
: =LO==F O@A;@ KH=;A\; HJG\;A=F;Q D=N=DK 9J= L@= <A>>=J=F;=K KALM9L=<
 !G E=9KMJ=K G> D=PA;9D KQFL9;LA; 9F< EGJH@GDG?A;9D ;GEHD=PALQ ;GJJ=D9L= OAL@ ) HJG\;A=F;Q
9 4@A;@ AF<ANA<M9D ;GEHD=PALQ E=9KMJ=K ;GJJ=D9L= :=KL OAL@ ) HJG\;A=F;Q
: 4@A;@ ;GE:AF9LAGF G> ;GEHD=PALQ E=9KMJ=K :=KL HJ=<A;LK ) HJG\;A=F;Q D=N=D
4. Material and methods
4.1. Dataset and participants
,MJ <9L9K=L ;GFKAKLK G>  K9EHD=K >JGE L@= International English Language Testing System (IELTS KH=9CAF? L=KL H=JL9AFAF? LG \N=
9<B9;=FL HJG\;A=F;Q D=N=DK 1@= &")10 =P9E AK 9 @A?@KL9C=K "F?DAK@ L=KL <=N=DGH=< :Q L@= JALAK@ GMF;AD 9F< 9E:JA<?= KK=KKE=FL
"F?DAK@ )=9JF=JK O@G L9C= L@= &")10 =P9E <G KG E9AFDQ >GJ AEEA?J9LAGF 9F< KLM<Q HMJHGK=K ;=JL9AF MFAN=JKALA=K AF =? L@= 2( 9F<
MKLJ9DA9 J=IMAJ= 9 EAFAEME &")10 K;GJ= LG =FL=J 1@= &")10 =P9E E=9KMJ=K "F?DAK@ D9F?M9?= HJG\;A=F;Q GF 9 K;9D= L@9L J9F?=K >JGE
:9F<  LG :9F< 1@= D=9JF=JK AF L@AK KLM<Q :=DGF? LG :9F<   K9EHD=K :9F<   K9EHD=K :9F<   K9EHD=K :9F<  
K9EHD=K 9F< :9F<  K9EHD=K 1@=K= :9F< D=N=DK @9N= :==F DGGK=DQ J=D9L=< LG L@= HJG\;A=F;Q D=N=DK <=K;JA:=< AF L@= GEEGF
"MJGH=9F #J9E=OGJC G> )9F?M9?=K1@= K9EHD=K AF GMJ ;GJHMK 9J= HJG<M;=< :Q D=9JF=JK H=JL9AFAF? LG "#/ D=N=DK  LG  1@=
;GJHMK ;GFKAKLK G> GF= K9EHD= H=J H9JLA;AH9FL 9F< L@= H9JLA;AH9FLK ;GE= >JGE <A>>=J=FL \JKLD9F?M9?= :9;C?JGMF<K OAL@ KGE= D9F
?M9?=K :=AF? EGJ= >J=IM=FL L@9F GL@=JK KM;@ 9K J9:A; @AF=K= GJ 19?9DG?
1@= KH=9CAF? L=KL L9C=K L@= >GJE G> 9F AFL=JNA=O :=LO==F 9 ;9F<A<9L= 9F< 9F =P9EAF=J O@A;@ D9KLK >GJ  EAFML=K &F L@= K=;
GF< H9JL G> L@= L=KL L@= ;9F<A<9L= AK J=IMAJ=< LG KH=9C 9:GML 9 LGHA; >GJ MH LG LOG EAFML=K &L AK L@AK EGFGDG?M= GJ DGF? LMJF O@A;@
O= 9F9DQK=< >GJ L@= HJ=K=FL KLM<Q 9F<A<9L=K 9J= ?AN=F 9 LGHA; 9F< L@=Q J=;=AN= GF= EAFML= LG HJ=H9J= O@9L L@=Q 9J= ?GAF? LG K9Q
"P9EHD=K G> LGHA;K 9J= <=K;JA:= GF= G> QGMJ F=A?@:GMJK<=K;JA:= KGE= LJ9N=DDAF? QGM OGMD< DAC= LG <G AF L@= >MLMJ=GJ <=K;JA:=
9 :MAD<AF? L@9L QGM DAC= 1@= KH=9CAF? L=KL AK K;GJ=< :Q E=9FK G> 9 JM:JA; 9F< L@= :9F< D=N=D AK ;9D;MD9L=< :Q 9N=J9?AF? L@= K;GJ=K GF
>GMJ <A>>=J=FL 9KH=;LK ]M=F;Q 9F< ;G@=J=F;= D=PA;9D J=KGMJ;= ?J9EE9LA;9D J9F?= 9F< 9;;MJ9;Q 9F< HJGFMF;A9LAGF
4.2. Complexity measures
4= ;9D;MD9L=< 9 LGL9D G> FAF= ;GEHD=PALQ E=9KMJ=K L9HHAF? AFLG KQFL9;LA;  D=PA;9D  9F< EGJH@GDG?A;9D ;GEHD=PALQ  19:D=
 HJGNA<=K 9F GN=JNA=O G> L@= E=9KMJ=K 9F< L@=AJ ;9D;MD9LAGF
1@= KQFL9;LA; ;GEHD=PALQ E=9KMJ=K L9J?=L L@= >GDDGOAF? @A=J9J;@A;9DDQ KLJM;LMJ=< HJG<M;LAGF MFALK 0MFALK ;D9MK=K 9F< H@J9K=K
D9MK=K 9J= ;GE:AF=< AFLG 0MFALK :Q E=9FK G> KM:GJ<AF9LAGF AF LMJF FGMF H@J9K=K 9J= 9 ;GFKLALM=FL ;GEHGF=FL G> ;D9MK=K DD KQF
L9;LA; E=9KMJ=K ;9D;MD9L=< AF L@AK KLM<Q 9J= GH=J9LAGF9DAK=< 9K J9LAGK 9F< L9J?=L =AL@=J L@= D=F?L@ G> HJG<M;LAGF MFALK A= FME:=J G>
OGJ<K H=J 0MFAL ;D9MK= GJ FGMF H@J9K= GJ L@= HJGHGJLAGF G> ;=JL9AF KH=;A\; KLJM;LMJ=K J=D9LAN= LG L@=AJ H9J=FL;9L=?GJQ A= FME
:=J G> KM:;D9MK=K GJ ;GGJ<AF9L=< ;D9MK=K <ANA<=< :Q L@= LGL9D FME:=J G> ;D9MK=K
*=9F D=F?L@ G> 0MFAL *)0 AK L@= EGKL ?DG:9D KQFL9;LA; E=9KMJ= AF;DM<=< AF L@AK KLM<Q AF L@9L 0MFALK ;9F := E9<= DGF?=J :Q
9<<AF? EGJ= ;D9MK=K LG?=L@=J GJ :Q D=F?L@=FAF? L@= ;GFKLALM=FL ;D9MK=K GJ H@J9K=K F 0MFAL AK <=\F=< 9K 9 KAF?D= KH=9C=JK MLL=J
9F;= ;GFKAKLAF? G> 9F independent clauseor sub-clausal unit LG?=L@=J OAL@ 9FQ subordinate clause(s) 9KKG;A9L=< OAL@ =AL@=J#GKL=J =L 9D
 H  0MFALK 9J= 9J?M9:DQ EGJ= 9<9HL=< >GJ 9F9DQKAF? KHGC=F D9F?M9?= L@9F 1MFALK O@A;@ 9J= G>L=F MK=< AF L@= 9F9DQKAK
G> OJALL=F <9L9 DKG >GJ L@= A<=FLA\;9LAGF G> ;D9MK=K 9F< KM:;D9MK=K O= >GDDGO L@= ?MA<=DAF=K HJGNA<=< :Q #GKL=J =L 9D  #GJ L@=
;GGJ<AF9LAGF J9LAG O= GFDQ ;GMFL AF<=H=F<=FL ;GGJ<AF9L=< ;D9MK=K *GJ= <=L9ADK 9:GML L@= ;9D;MD9LAGF G> E=9F FGMF H@J9K= D=F?L@ 9J=
HJGNA<=< AF MDLV  %GMK=F 
&F HJ9;LA;= &")10 <G=K FGL MK= D=N=DK 
@LLHKOOOA=DLKGJ?A=DLK>GJGJ?9FAK9LAGFK;GEEGF=MJGH=9F>J9E=OGJC
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246
Table 2
GEHD=PALQ E=9KMJ=K
*=9KMJ= 9D;MD9LAGF
Syntactic complexity
*=9FD=F?L@G>0MFAL*)0 OGJ<K0MFALK
0M:;D9MK=J9LAG0 / KM:;D9MK=K;D9MK=K
*=9FD=F?L@G>;D9MK=*)  OGJ<K;D9MK=K
GGJ<AF9LAGFJ9LAG / AF<=H=F<=FL;GGJ<AF9L=<;D9MK=K;D9MK=K
*=9FD=F?L@G>FGMFH@J9K=*)+- OGJ<KAFFGMFH@J9K=KFGMFH@J9K=K
Lexical complexity
$MAJ9M<KAF<=P$ LQH=K3LGC=FK
%QH=J?=GE=LJA;<AKLJA:MLAGF%!! K== *; 9JL@Q9F<'9JNAK
*=9KMJ=G>L=PLM9DD=PA;9D<AN=JKALQ*1)! K== *; 9JL@Q9F<'9JNAK
Morphological complexity
*GJH@GDG?A;9D;GEHD=PALQAF<=PN=J:K* & K== J=RAF99F<-9DDGLLA
1@= L@J== E=9KMJ=K G> D=PA;9D ;GEHD=PALQ 9J= 9DD N9JA9LAGFK G> L@= D=PA;9D LQH=LGC=F J9LAG 11/ L@9L LJQ LG ;GEH=FK9L= >GJ MFO9FL=<
L=PLD=F?L@ =>>=;LK A= L@= DGF?=J 9 L=PL AK L@= @A?@=J L@= HJG:9:ADALQ L@9L OGJ<K 9J= J=H=9L=< $MAJ9M<K AF<=P G>>=JK L@= EGKL KAEHD=
LJ9FK>GJE9LAGF AF L@9L 9 KIM9J= JGGL AK 9<<=< LG L@= <=FGEAF9LGJ G> L@= KAEHD= 11/ >GJEMD9 $MAJ9M<  1@AK LJ9FK>GJE9LAGF
9;LM9DDQ GN=J;GEH=FK9L=K >GJ L@= =>>=;LK G> L=PL D=F?L@ 9F< DGF?=J L=PLK L=F< LG ?=L @A?@=J K;GJ=K GF $MAJ9M<K AF<=P L@9F K@GJL=J L=PLK
MDLV %GMK=F -A=JJ9J<  39F !9=D=  1@MK $MAJ9M<K AF<=P L9HK AFLG L@J== <AKLAF;L 9KH=;LK G> D=PA;9D <AN=JKALQ F9E=DQ KAR= A=
OGJ< LGC=FK JA;@F=KK A= OGJ< LQH=K 9F< L@= =>>=;LAN= FME:=J G> LQH=K '9JNAK  *1)! 9F< %!! :GL@ GFDQ L9J?=L L@= J9F?=
G> <A>>=J=FL OGJ<K AF 9 L=PL*; 9JL@Q '9JNAK  H  GJ AF GL@=J OGJ<K L@= =>>=;LAN= FME:=J G> LQH=K :Q J=DQAF? GF 9 EGJ=
;GEHDA;9L=< 9F< E9L@=E9LA;9DDQ KH=9CAF? EGJ= ;GJJ=;L LJ9FK>GJE9LAGF G> L@= 11/ LG ;GEH=FK9L= >GJ L=PL D=F?L@ =>>=;LK *; 9JL@Q
'9JNAK  
*GJH@GDG?A;9D ;GEHD=PALQ AK E=9KMJ=< :Q E=9FK G> L@= EGJH@GDG?A;9D ;GEHD=PALQ AF<=P * & 9HHDA=< LG N=J:K J=RAF9 -9DDGLLA
 1@AK AF<=P O@GK= MF<=JDQAF? DG?A; AK KAEAD9J LG L@9L G> D=PA;9D 11/K L9J?=LK L@= AF]=;LAGF9D <AN=JKALQ G> N=J: >GJEK AF 9 L=PL :Q
9F9DQKAF? L@= FME:=J G> <A>>=J=FL EGJH@GDG?A;9D HJG;=KK=K GJ =PHGF=FLK L@9L 9J= 9HHDA=< &LK ;GEHML9LAGF AK :9K=< GF J=H=9L=< J9F
<GE K9EHDAF? >JGE 9DD =PHGF=FLK AF 9 L=PL 9F< ;GMFLAF? L@= 9N=J9?= FME:=J G> <A>>=J=FL =PHGF=FLK OAL@AF 9F< 9;JGKK L@=K= K9EHD=K
Q C==HAF? L@= KAR= G> L@= J9F<GE K9EHD=K ;GFKL9FL MFO9FL=< L=PL D=F?L@ =>>=;LK 9J= =DAEAF9L=< F * & N9DM= G> E=9FK L@9L 9DD N=J:
>GJEK AF L@= L=PL 9J= L@= K9E= EGJH@GDG?A;9DDQ KH=9CAF? 9F< @A?@=J N9DM=K AF<A;9L= L@9L 9 L=PL ;GFL9AFK EGJ= <A>>=J=FL EGJH@GDG?A;9D
N=J: >GJEK 1@= L@=GJ=LA;9D E9PAEME N9DM= >GJ L@AK E=9KMJ= O@A;@ <=H=F<K GF L@= K=D=;L=< K9EHD= KAR= AK  AF L@AK KLM<Q
4.3. Data coding and analysis
+=9JDQ 9DD 9M<AG \D=K HJGNA<=< :Q &")10 O=J= 9DJ=9<Q 9;;GEH9FA=< :Q LJ9FK;JAHLAGFK 9F< L@= J=E9AFAF? GF=K O=J= LJ9FK;JA:=< :Q
L@= K=;GF< 9ML@GJ 1@= LJ9FK;JAHLAGFK O=J= IMAL= <=L9AD=< 9K L@=Q ;GFL9AF=< AF>GJE9LAGF 9:GML >GJ =P9EHD= K=FL=F;= KLJ=KK H9MK=
D=F?L@ @=KAL9LAGFK 9F< >9DK= KL9JLK !9L9 HJ=H9J9LAGF ;GFKAKL=< AF J=EGNAF? @=KAL9LAGF E9JC=JK =JE 9F< AFL=JB=;LAGFK KM;@ 9K Q=9@
QGM CFGO O=DD >9DK= KL9JLK >GJ AFKL9F;= 9K KA9F O= 9J= >J== LG ?G LG =FL=J %GF? (GF?:=;GE=K 9K KA9F O= 9J= >J== LG =FL=J
%GF? (GF? 9F< J=H=LALAGFK >GJ AFKL9F;= &LK 9 DGL G> >MF O@=F QGM O@=F QGM LJ9N=D 0GE= AF9M<A:D= GJ MF;D=9J >J9?E=FLK 9DKG @9<
LG := D=>L GML
&F 9 F=PL KL=H L@= K9EHD=K O=J= <ANA<=< AFLG 0MFALK K== <=>AFALAGF 9:GN= 9F< ;D9MK=K #GDDGOAF? #GKL=J =L 9D  O= ;GFKA<
=J=< FGF\FAL= ;D9MK=K LG := K=H9J9L= ;D9MK=K A> L@=Q ;GFL9AF=< 9 N=J: 9F< 9L D=9KL GF= GL@=J =D=E=FL #GJ =P9EHD= &LK 9 ?GG< HD9;=
LG DAN= :9F< O9K 9F9DQK=< 9K GF= ;D9MK= O@AD= ,F= <9Q K@= 9KC E=LG @=DH @=J :9F< O9K <ANA<=< AFLG LOG ;D9MK=K 1@= L=PLK
O=J= E9FM9DDQ ;G<=< >GJ KQFL9;LA; >=9LMJ=K :Q L@= K=;GF< 9ML@GJ AF ;9K= G> <GM:L 9>L=J <AK;MKKAGF OAL@ L@= \JKL 9ML@GJ 1G =KL9:DAK@
AFL=J;G<=J J=DA9:ADALQ  J9F<GEDQ K=D=;L=< L=PLK A= KDA?@LDQ GN=J  G> L@= ;GJHMK O=J= ;G<=< K=H9J9L=DQ :Q L@= \JKL 9ML@GJ 1@=
;GJJ=D9LAGFK :=LO==F L@= LOG ;G<AF?K J9F?=< >JGE  >GJ *)+- LG  >GJ *) 1@= LGGD >GJ L@= 9MLGE9LA; 9F9DQKAK G> D=PA;9D
<AN=JKALQ 1)"! O9K MK=< >GJ L@= D=PA;9D 9F9DQK=K 9F< L@= * & O9K ;9D;MD9L=< OAL@ L@= ;GEHML=J LGGD <=N=DGH=< :Q J=RAF9 9F<
-9DDGLLA 
4= OGJC OAL@  J9F<GE K9EHD=K G>  =PHGF=FLK =9;@
0 /  *)0  / 
OOODAF?MAKLA;9F9DQKAKLGGDKGJ? N=JKAGF 
@LLH;GJHGJ9D9F;K9;MCNG;9:9F9DQK=8EGJH@H@H 9DH@9 N=JKAGF
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246
4.4. Statistical analyses
4= MK=< +,3K OAL@  H9AJOAK= ;GEH9JAKGFK D=9KL KA?FA>A;9FL <A>>=J=F;= LG 9KK=KK <A>>=J=F;=K :=LO==F L@= \N= &")10 HJG
\;A=F;Q D=N=DK )=N=F=K L=KL K@GO=< L@9L GFDQ >GJ GF= G> L@= E=9KMJ=K E=9F D=F?L@ G> 0MFAL L@= 9KKMEHLAGF G> @GEG?=F=ALQ G>
N9JA9F;=K O9K FGL E=L H   E9AFDQ <M= LG 9 EM;@ D9J?=J N9JA9:ADALQ AF L@= @A?@=KL HJG\;A=F;Q D=N=D#GJ L@= K9C= G> ;GFKAK
L=F;Q O= <=;A<=< LG MK= KL9F<9J< +,3K >GJ =9;@ G> L@= E=9KMJ=K 9DKG ;GFKA<=JAF? L@= N=JQ KAEAD9J ?JGMH KAR=K O@A;@ HGKALAN=DQ
9>>=;LK L@= GN=J9DD JG:MKLF=KK G> L@= 9F9DQK=K 1@= E9AF +,3K O=J= MK=< LG =KLAE9L= O@=L@=J L@= GN=J9DD =>>=;L G> HJG\;A=F;Q D=N=D
GF L@= N9JAGMK ;GEHD=PALQ K;GJ=K O9K KA?FA>A;9FL 9F< O@9L L@= KAR= G> L@AK =>>=;L O9K E=9KMJ=< OAL@ =L9 1@= H9AJOAK= ;GEH9JAKGFK
HJGNA<= EGJ= AF>GJE9LAGF 9:GML L@= KH=;A\; DG;9LAGF G> L@= =>>=;L 4= <G FGL 9HHDQ ;GJJ=;LAGFK >GJ EMDLAHD= L=KLAF? =? GF>=JJGFA
KAF;= L@= ;GEH9JAKGFK 9J= HD9FF=< 9F< FGL E=9FL >GJ @QHGL@=KAK L=KLAF? AF 9 F9JJGO K=FK= &F 9<<ALAGF L@= KAR= G> GMJ KM:K9EHD=K H=J
HJG\;A=F;Q D=N=D AK J=D9LAN=DQ KE9DD Q=L 9DEGKL A<=FLA;9D K 9 J=KMDL L@= J=HGJL=< HN9DM=K K@GMD< FGL := AFL=JHJ=L=< 9:KGDML=DQ :ML
J9L@=J 9K HJGNA<AF? AF<A;9LAGFK G> L@= HJ=;AK= DG;9LAGF G> KAR=9:D= <A>>=J=F;=K :=LO==F HJG\;A=F;Q D=N=DK
&F 9 K=;GF< KL=H O= MK= ;GJJ=D9LAGF 9F9DQK=K 9K O=DD 9K GJ<AF9D DG?AKLA; J=?J=KKAGF LG 9K;=JL9AF O@A;@ ;GE:AF9LAGFK G> E=9KMJ=K
K@GO L@= KLJGF?=KL J=D9LAGFK@AH OAL@ HJG\;A=F;Q D=N=D 4= MK= 0H=9JE9F J9FC ;GJJ=D9LAGFK LG L=KL L@= KLJ=F?L@ G> L@= 9KKG;A9LAGF :=
LO==F HJG\;A=F;Q D=N=D 9F< =9;@ G> L@= ;GEHD=PALQ E=9KMJ=K 4= L@=F \L 9 ;MEMD9LAN= DG?AL EG<=D OAL@ HJGHGJLAGF9D G<<K LG L@= <9L9
MKAF? -/, ),$&01& AF 00 0M;@ 9 EG<=D AEHGK=K =IM9D KDGH=K LG := =KLAE9L=< >GJ =9;@ J=KHGFK= >MF;LAGF GFDQ L@= AFL=J;=HLK 9J=
9DDGO=< LG N9JQ =N=F L@GM?@ L@=Q 9J= ;GFKLJ9AF=< LG AF;J=9K= ?J=KLA  !=JJ  &F GL@=J OGJ<K L@= =>>=;LK G> L@= HJ=<A;LGJK
9J= 9KKME=< LG := L@= K9E= >GJ =9;@ 9<B9;=FL H9AJ G> HJG\;A=F;Q D=N=DK 1@= HJGHGJLAGF9D G<<K 9KKMEHLAGF AK L=KL=< :Q E=9FK G> 9 K;GJ=
L=KL 4= J=HGJL +9?=DC=JC=K /9K 9F 9HHJGPAE9LAGF G> L@= /KL9LAKLA; MK=< LG AF<A;9L= L@= HJGHGJLAGF G> =PHD9AF=< N9JA9F;= AF DAF=9J
J=?J=KKAGF EG<=DK -JG\;A=F;Q D=N=D AK MK=< 9K <=H=F<=FL N9JA9:D= AF L@AK GJ<AF9D DG?AKLA; J=?J=KKAGF EG<=D 9F< ;GEHD=PALQ E=9KMJ=K
9J= =FL=J=< 9K AF<=H=F<=FL N9JA9:D=K 1G 9NGA< EMDLA;GDDAF=9JALQ @A?@DQ ;GJJ=D9LAF? ;GEHD=PALQ E=9KMJ=K A= r  9J= D=>L GML G>
L@= EG<=D
5. Results
5.1. Can complexity measures discriminate between L2 pro>ciency levels?
&F L@AK K=;LAGF O= J=HGJL L@= J=KMDLK G> L@= +,3K 9F< H9AJOAK= ;GEH9JAKGFK 1@= <=K;JAHLAN= KL9LAKLA;K >GJ 9DD E=9KMJ=K E=9F 9F<
KL9F<9J< <=NA9LAGF H=J HJG\;A=F;Q D=N=D 9F< GN=J9DD 9J= HJGNA<=< AF HH=F<AP  HH=F<AP  ;GFL9AFK 9F GN=JNA=O G> L@= J=KMDLK G>
L@= +,3K #GJ =9;@ ;GEHD=PALQ E=9KMJ= O= KMEE9JAK= L@= J=KMDLK :Q E=9FK G> 9 :9J ;@9JL K@GOAF? L@= E=9F K;GJ= H=J HJG\;A=F;Q
D=N=D KMJJGMF<=< :Q 9  ;GF\<=F;= AFL=JN9D 9K O=DD 9K HGL=FLA9D KA?FA>A;9FL <A>>=J=F;=K :=LO==F H9AJK G> HJG\;A=F;Q D=N=DK 
H9AJK AF LGL9D H=J 9F9DQKAK AF<A;9L=< AF L@= LGH H9JL G> L@= ?J9H@
,N=J9DD E=9F 0MFAL D=F?L@ <A>>=J=< KA?FA>A;9FLDQ 9;JGKK HJG\;A=F;Q D=N=DK #   H   η  #A?  K@GOK
L@9L L@= E=9F D=F?L@ G> 0MFALK KL=9<ADQ AF;J=9K=K >JGE 9JGMF< FAF= 9F< 9 @9D> OGJ<K AF D=N=D  LG GN=J  OGJ<K AF D=N=D  0=N=F
GML G>  H9AJOAK= ;GEH9JAKGFK K@GO=< KAR=9:D= <A>>=J=F;=K :=LO==F HJG\;A=F;Q D=N=DK 6=L GFDQ >GJ GF= H9AJ G> 9<B9;=FL HJG\;A=F;Q
D=N=DK D=N=DK  9F<  9 KAR=9:D= <A>>=J=F;= O9K >GMF<
DKG >GJ L@= KM:;D9MK= J9LAG L@= K;GJ=K <A>>=J=< KA?FA>A;9FLDQ 9;JGKK HJG\;A=F;Q D=N=DK #   H   η  #A?
 K@GOK L@9L 9JGMF<  G> L@= ;D9MK=K HJG<M;=< :Q L@= D=9JF=JK 9L D=N=D  O9K KM:GJ<AF9L=< Q D=N=D  L@AK HJGHGJLAGF @9< AF;J=9K=<
LG GN=J  "N=F L@GM?@ L@=J= AK 9 ;D=9J AF;J=9KAF? LJ=F< AF 0 / K;GJ=K OAL@ AF;J=9KAF? HJG\;A=F;Q D=N=D GFDQ >GMJ H9AJOAK= <A>>=J
=F;=K :=LO==F D=N=DK O=J= >GMF< LG := KA?FA>A;9FL +G KAR=9:D= <A>>=J=F;=K :=LO==F 9<B9;=FL D=N=DK O=J= G:K=JN=< 1@= K;GJ=K >GJ L@=
D=9JF=JK AF L@= @A?@=KL HJG\;A=F;Q D=N=D <A>>=J=< ;GFKA<=J9:DQ >JGE L@= K;GJ=K AF 9DD D=N=DK =P;=HL >GJ D=N=D 
1@= E=9F ;D9MK= D=F?L@ <A>>=J=< KA?FA>A;9FLDQ :=LO==F HJG\;A=F;Q D=N=DK 9K O=DD #   H   η  K #A? 
K@GOK L@= AF;J=9K=K AF *) <G FGL >GDDGO 9 DAF=9J H9LL=JF 9;JGKK HJG\;A=F;Q D=N=DK &F L@= DGO=KL LOG HJG\;A=F;Q D=N=DK L@= 9N=J9?=
D=F?L@ G> L@= ;D9MK=K HJG<M;=< :Q D=9JF=JK AK 9JGMF< \N= 9F< 9 @9D> OGJ<K 1@AK N9DM= JAK=K LG 9DEGKL KAP OGJ<K AF D=N=D  9F< KDA?@LDQ
GN=J KAP 9F< 9 @9D> AF D=N=D  &F D=N=D  *) N9DM=K <JGH 9?9AF LG L@= D=N=D G> D=N=D  1@= H9AJOAK= ;GEH9JAKGFK K@GO L@9L *) N9DM=K
9J= ;GFKA<=J9:DQ @A?@=J AF D=N=D  L@9F AF D=N=DK   9F< L@= 9<B9;=FL D=N=D  +G KAR=9:D= <A>>=J=F;= O9K >GMF< :=LO==F D=N=DK  9F< 
#GJ L@= HJGHGJLAGF G> ;GGJ<AF9L=< ;D9MK=K O= <A< FGL G:K=JN= 9 KA?FA>A;9FL GN=J9DD <A>>=J=F;= :=LO==F HJG\;A=F;Q D=N=DK
#   H   η  0DA?@LDQ GN=J GF= GML G> \N= ;D9MK=K HJG<M;=< :Q L@= D=9JF=JK AF D=N=D  O9K ;GGJ<AF9L=< K==
#A?  1@AK HJGHGJLAGF JAK=K LG 9JGMF<  AF D=N=D  :ML L@=F <JGHK MFLAD AL J=9;@=K ALK DGO=KL HGAFL AF D=N=D  9JGMF<  ,FDQ
LOG KAR=9:D= <A>>=J=F;=K :=LO==F HJG\;A=F;Q D=N=DK O=J= G:K=JN=<  vs  9F<  vs 
#GJ L@= D9KL KQFL9;LA; ;GEHD=PALQ E=9KMJ= E=9F D=F?L@ G> FGMF H@J9K= L@= GN=J9DD <A>>=J=F;= :=LO==F HJG\;A=F;Q D=N=DK O9K KA?
FA>A;9FL #   H   η  )=9JF=JK AF D=N=D  HJG<M;= FGMF H@J9K=K OAL@ GF 9N=J9?= 9JGMF<  OGJ<K K==
#A?  &F D=N=DK  9F<  L@AK N9DM= @9K JAK=F LG 9JGMF<  9F< AF D=N=DK  9F<  AL AK ;DGK= LG L@J== 0AP KA?FA>A;9FL <A>>=J=F;=K :=
K AF<A;9L=< :Q L@= D9J?= ;GF\<=F;= AFL=JN9D >GJ L@AK HJG\;A=F;Q D=N=D AF #A? 
#GJ J=>=J=F;= OAL@  H9AJOAK= ;GEH9JAKGFK 9HHDQAF? GF>=JJGFAK ;GJJ=;LAGF OGMD< 9EGMFL LG <ANA<AF? L@= L@J=K@GD< >GJ KA?FA>A;9F;= αD=N=D :Q  =?
α  :=;GE=K α 
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246
Fig. 1. *=9F D=F?L@ G> 0MFAL K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H    H    H  
Fig. 2. 0M:;D9MK= J9LAG K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H    H    H  
Fig. 3. *=9F D=F?L@ G> ;D9MK= K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H    H    H  
LO==F H9AJK G> HJG\;A=F;Q D=N=DK O=J= >GMF< 1@= H9AJOAK= ;GEH9JAKGFK ;D=9JDQ K@GO L@9L *)+- K;GJ=K ;9F := <ANA<=< AFLG LOG <AKLAF;L
?JGMHK D=N=DK   9F<  GF L@= GF= @9F< 9F< D=N=DK  9F<  GF L@= GL@=J
1MJFAF? LG E=9KMJ=K G> D=PA;9D ;GEHD=PALQ >GJ $MAJ9M<K AF<=P 9 KA?FA>A;9FL GN=J9DD =>>=;L G> HJG\;A=F;Q D=N=D O9K >GMF<
#   H   η  K #A?  K@GOK L@= D=9JF=JK AF D=N=DK  9F<  G:L9AF K;GJ=K G> 9JGMF<  9F< L@AK N9DM=
JAK=K OAL@ 9HHJGPAE9L=DQ  HGAFLK :=LO==F L@= J=E9AFAF? ;GFK=;MLAN= D=N=DK LG 9JGMF<  AF D=N=D  &F LGL9D =A?@L KAR=9:D= <A>>=J
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246
=F;=K O=J= >GMF< :=LO==F HJG\;A=F;Q D=N=DK 4= >GMF< <A>>=J=F;=K >GJ LOG 9<B9;=FL H9AJK G> HJG\;A=F;Q D=N=DK  vs  9F<  vs  GL@
D=N=DK  9F<  <A>>=J ;GFKA<=J9:DQ >JGE 9DD GL@=J HJG\;A=F;Q D=N=DK 9F< 9DKG L@= <A>>=J=F;= :=LO==F D=N=DK  9F<  AK KA?FA>A;9FL
1@= GN=J9DD H9LL=JF >GJ %!! L@= K=;GF< D=PA;9D ;GEHD=PALQ E=9KMJ= AK >9AJDQ KAEAD9J LG L@= GF= O= G:K=JN=< >GJ $MAJ9M<K AF<=P
K== #A?  DKG @=J= L@= GN=J9DD =>>=;L G> HJG\;A=F;Q D=N=D AK KA?FA>A;9FL #   H   η  =N=F L@GM?@ L@=
=>>=;L KAR= AK ;GFKA<=J9:DQ KE9DD=J %!! K;GJ=K ;GFKAKL=FLDQ JAK= >JGE  LG  >JGE D=N=D  LG D=N=D  &F ;GFLJ9KL LG $MAJ9M<K AF
<=P FG ;GFKA<=J9:D= <A>>=J=F;= O9K >GMF< :=LO==F D=N=DK  9F<  :ML 9DD GL@=J H9AJK L@9L QA=D<=< KA?FA>A;9FL <A>>=J=F;=K >GJ $MAJ9M<K
AF<=P 9DKG <G KG >GJ %!!
#GJ *1)! L@= \F9D D=PA;9D ;GEHD=PALQ E=9KMJ= O= 9DKG >GMF< 9 KA?FA>A;9FL GN=J9DD =>>=;L G> HJG\;A=F;Q D=N=D GF L@= K;GJ=K
#   H   η  1@= DGO=J =>>=;L KAR= ;GEH9J=< LG $MAJ9M<K AF<=P 9F< %!! AK 9DKG J=]=;L=< AF L@= KDA?@LDQ
>=O=J 9F< D=KK KLJGF?DQ KA?FA>A;9FL H9AJOAK= ;GEH9JAKGFK #GJ *1)! O= <A< FGL \F< ;GFKA<=J9:D= <A>>=J=F;=K :=LO==F 9<B9;=FL D=N=DK
AF KHAL= G> ;GFKAKL=FLDQ JAKAF? K;GJ=K OAL@ JAKAF? HJG\;A=F;Q D=N=D AF;J=9KAF? >JGE 9JGMF<  AF D=N=D  LG 9JGMF<  AF D=N=D  K== #A?

#AF9DDQ O= DGGC 9L L@= J=KMDLK >GJ * & GMJ E=9KMJ= G> EGJH@GDG?A;9D ;GEHD=PALQ 1@= GN=J9DD <A>>=J=F;= :=LO==F HJG\;A=F;Q D=N=DK
AK KA?FA>A;9FL #   H   η  &L AK ;D=9J >JGE #A? L@9L L@= G:K=JN=< <A>>=J=F;= E9AFDQ DA=K :=LO==F L@=
DGO=KL HJG\;A=F;Q D=N=D 9F< 9DD GL@=J D=N=DK ;GE:AF=< 1@= GFDQ ;GFKA<=J9:D= H9AJOAK= <A>>=J=F;=K 9J= G:K=JN=< :=LO==F D=N=D  9F<
9DD GL@=J D=N=DK 1@AK E=9FK L@9L 9DKG L@= <A>>=J=F;= :=LO==F L@= 9<B9;=FL D=N=DK  9F<  AK KA?FA>A;9FL
5.2. Which complexity measures correlate best with L2 pro>ciency?
&F GJ<=J LG =N9DM9L= O@A;@ ;GEHD=PALQ E=9KMJ=K K@GO L@= KLJGF?=KL =>>=;L G> ) HJG\;A=F;Q D=N=D O= ;9D;MD9L=< 0H=9JE9F ;GJJ=
D9LAGF ;G=>\;A=FLK :=LO==F L@= K;GJ=K GF =9;@ E=9KMJ= 9F< L@= HJG\;A=F;Q D=N=D G> L@= D=9JF=JK 19:D=  K@GOK L@9L L@= ;GJJ=D9LAGF
AK KA?FA>A;9FL 9F< HGKALAN= >GJ =A?@L GML G> FAF= E=9KMJ=K OAL@ L@= KLJGF?=KL ;GJJ=D9LAGFK >GMF< >GJ $MAJ9M<K AF<=P ρ  >GD
DGO=< :Q LOG KQFL9;LA; E=9KMJ=K *)+- 9F< *)0 OAL@ ρ  9F< ρ  9F< 9FGL@=J D=PA;9D E=9KMJ= %!! ρ 
,FDQ >GJ L@= ;GGJ<AF9LAGF J9LAG L@= ;GJJ=D9LAGF ;G=>\;A=FL O9K FGL KA?FA>A;9FL 1@AK AK FGL KMJHJAKAF? KAF;= L@= K;GJ=K GF L@AK E=9KMJ=
>GDDGO 9F AFN=JL=<3K@9H=< J9L@=J L@9F 9 DAF=9J H9LL=JF K== #A? 
HH=F<AP K@GOK L@= -=9JKGF ;GJJ=D9LAGFK :=LO==F L@= <A>>=J=FL ;GEHD=PALQ E=9KMJ=K *9FQ G> L@=K= ;GJJ=D9LAGFK 9J= HGKALAN= 9F<
KA?FA>A;9FL O@A;@ 9L D=9KL AF H9JL ;9F := 9LLJA:ML=< LG L@=AJ K@9J=< ;GJJ=D9LAGF OAL@ HJG\;A=F;Q 1@= @A?@=KL ;GJJ=D9LAGFK 9J= >GMF<
:=LO==F L@= D=PA;9D ;GEHD=PALQ E=9KMJ=K %!! 9F< $ r  9F< %!! 9F< *1)! r  O@A;@ 9DD L9J?=L D=PA;9D <AN=J
KALQ DKG L@= ;GJJ=D9LAGF :=LO==F L@= KQFL9;LA; E=9KMJ=K *)0 9F< 0 / AK @A?@ r  O@A;@ AK FGL KMJHJAKAF? ;GFKA<=JAF? L@=
KLJM;LMJ9D AFL=J;GFF=;L=<F=KK G> L@=K= LOG E=9KMJ=K A= 0MFALK ;9F := E9<= DGF?=J :Q AF;DM<AF? EGJ= KM:;D9MK=K 4= 9DKG >GMF<
LOG KA?FA>A;9FLDQ F=?9LAN= ;GJJ=D9LAGFK :=LO==F / GF L@= GF= @9F< 9F< 0 / r 9F< *)0 r GF L@= GL@=J
J=]=;LAF? L@9L KH=9C=JK @9N= LG ;@GGK= :=LO==F ;GGJ<AF9LAGF 9F< KM:GJ<AF9LAGF 9K ;D9MK=DAFCAF? E=;@9FAKE
GFKA<=JAF? ALK @A?@ ;GJJ=D9LAGF OAL@ :GL@ $ 9F< *1)! O= <A< FGL AF;DM<= %!! AF L@= GJ<AF9D DG?AKLA; J=?J=KKAGF EG<=D OAL@
HJG\;A=F;Q D=N=D 9K <=H=F<=FL N9JA9:D= DKG *)0 O9K D=>L GML <M= LG @A?@ ;GJJ=D9LAGFK OAL@ 0 / 9F< LG 9 KGE=O@9L D=KK=J =PL=FL
*)+- #AF9DDQ O= 9DKG <A< FGL AF;DM<= / KAF;= L@AK E=9KMJ= O9K >GMF< LG @9N= 9 ;D=9JDQ FGFDAF=9J J=D9LAGFK@AH OAL@ HJG\;A=F;Q
1@= K;GJ= L=KL <G=K FGL AF<A;9L= L@9L L@= HJGHGJLAGF9D G<<K 9KKMEHLAGF G> GMJ ;MEMD9LAN= DG?AL EG<=D AK NAGD9L=< χ  <>  
H   +9?=DC=JC=K /G>  AF<A;9L=K L@9L 9JGMF< LOG L@AJ<K G> L@= N9JA9F;= AF HJG\;A=F;Q D=N=D AK =PHD9AF=< :Q L@= EG<=D
19:D=  ;GFL9AFK L@= H9J9E=L=J =KLAE9L=K >GJ L@= GJ<AF9D DG?AKLA; J=?J=KKAGF EG<=D
1@= EG<=D ;GFL9AFK L@J== KA?FA>A;9FL HJ=<A;LGJK $ 0 / 9F< * & =9;@ L9J?=LAF? ;GEHD=PALQ AF 9 <A>>=J=FL DAF?MAKLA; <GE9AF A=
D=PA;9D KQFL9;LA; 9F< EGJH@GDG?A;9D ,> L@=K= L@J== $ AK L@= KLJGF?=KL HJ=<A;LGJ β >GDDGO=< :Q 0 / β 9F< * &
β 1@= ;GFLJA:MLAGFK G> L@= L@J== J=E9AFAF? HJ=<A;LGJK *)  *)+- 9F< *1)! 9J= FGL KA?FA>A;9FL AF L@= EG<=D
6. Discussion
6.1. Can complexity measures discriminate between pro>ciency levels?
$=F=J9DDQ KH=9CAF? L@= J=KMDLK G> L@AK KLM<Q ;GF\JE L@9L ) KH==;@ ;GEHD=PALQ E=9KMJ=K ;9F <AK;JAEAF9L= :=LO==F D=9JF=JK 9L <A>
>=J=FL HJG\;A=F;Q D=N=DK =N=F L@GM?@ O= 9DKG G:K=JN=< ;GFKA<=J9:D= <A>>=J=F;=K 9;JGKK E=9KMJ=K 9F< 9;JGKK HJG\;A=F;Q D=N=DK )GGCAF?
EGJ= ;DGK=DQ 9L L@= J=KMDLK H=J ;GEHD=PALQ <AE=FKAGF GMJ \F<AF? L@9L EGJH@GDG?A;9D ;GEHD=PALQ ;GMD< GFDQ <A>>=J=FLA9L= :=LO==F L@=
DGO=KL D=N=D 9F< 9DD @A?@=J D=N=DK AK AF DAF= OAL@ != D=J;I 9F< %GMK=F  HGL=FLA9D =PHD9F9LAGF >GJ L@AK AK L@= DAEAL=< J9F?= G>
AF]=;LAGF9D EGJH@GDG?Q 9>>=;LAF? L@= N=J:9D KQKL=E AF HJ=K=FL<9Q "F?DAK@ J=KMDLAF? AF 9 DAEAL=< FME:=J G> HGKKA:D= >GJEK J=RAF9
 -9DDGLLA  +=N=JL@=D=KK EGJH@GDG?A;9D ;GEHD=PALQ 9F< L@= EGJH@GDG?A;9D ;GEHD=PALQ AF<=P AF H9JLA;MD9J 9HH=9JK LG := 9F
9HHJGHJA9L= AF<A;9LGJ G> "F?DAK@ ) HJG\;A=F;Q 9L =9JDQ KL9?=K G> <=N=DGHE=FL
/=?9J<AF? D=PA;9D ;GEHD=PALQ GMJ KLM<Q ;GF\JEK L@9L D=PA;9D <AN=JKALQ E=9KMJ=K $MAJ9M<K AF<=P 9F< %!! AF H9JLA;MD9J 9J= 9:D=
LG <AK;JAEAF9L= :=LO==F 9<B9;=FL HJG\;A=F;Q D=N=DK != D=J;I  )M  1@= L@J== D=PA;9D <AN=JKALQ E=9KMJ=K AF;DM<=< AF L@AK
KLM<Q K@GO=< 9 ?J9<M9D AF;J=9K= :=LO==F D=N=DK  LG  G> L@= &")10 KH=9CAF? L=KL O@A;@ ;GJJG:GJ9L=K /=9< 9F< +9LAGFK 
 &F 9;;GJ<9F;= OAL@ L@= <=>9MDL EG<=D KH=;A\;9LAGF AF 00 F=?9LAN= H9J9E=L=J =KLAE9L=K >GJ 9 HJ=<A;LGJ AF<A;9L= L@9L @A?@=J K;GJ=K >GJ L@= ;GJJ=KHGF<AF? ;GEHD=P
ALQ E=9KMJ= 9J= 9KKG;A9L=< OAL@ @A?@=J HJG\;A=F;Q D=N=DK
UNCORRECTED PROOF
 B. Bulté and H. Roothooft / System xxx (xxxx) 102246
Table 3
GJJ=D9LAGFK :=LO==F ;GEHD=PALQ E=9KMJ=K 9F< HJG\;A=F;Q D=N=D  H   H   H 
0H=9JE9F;GJJ=D9LAGF;G=^;A=FLρ
0QFL9;LA;;GEHD=PALQ
Mean length of AS-unit 
Subclause ratio 
Mean length of clause 
Coordination ratio 
Mean length of NP 
Lexical complexity
Guiraud's index 
HD-D 
MTLD 
Morphological complexity
MCI-verbs 
Fig. 4. GGJ<AF9LAGF J9LAG K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H   H   H 
Fig. 5. *=9F D=F?L@ G> +- K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H    H    H  
\F<AF?K *GJ=GN=J O= >GMF< L@9L 9DD <AN=JKALQ E=9KMJ=K ?9N= JAK= LG KA?FA>A;9FL <A>>=J=F;=K :=LO==F HJG\;A=F;Q D=N=DK :ML GFDQ
$MAJ9M<K AF<=P 9F< %!! ;GMD< <AK;JAEAF9L= :=LO==F KGE= 9<B9;=FL D=N=DK D=N=DK  9F<  9F<  9F<  >GJ $MAJ9M<K AF<=P 9F< GFDQ
D=N=DK 9F< >GJ %!! K AF != D=J;I  L@=J= O=J= FG KA?FA>A;9FL <A>>=J=F;=K AF D=PA;9D ;GEHD=PALQ :=LO==F L@= LOG @A?@=KL
D=N=DK  9F<  AF GMJ KLM<Q 1@AK @GO=N=J ;GFLJ9KLK OAL@ (9F?  O@G ;GF;DM<=< L@9L <A>>=J=F;=K AF D=PA;9D ;GEHD=PALQ E9AFDQ
E9FA>=KL=< L@=EK=DN=K :=LO==F "#/ D=N=DK  9F<  9F< 9F<  O@A;@ ;9F := K9A< LG ;GJJ=KHGF< LG &")10 :9F<K 9F<  &L
K@GMD< := FGL=< @=J= L@9L (9F?  9DKG AF;DM<=< E=9KMJ=K G> D=PA;9D <=FKALQ 9F< KGH@AKLA;9LAGF
#GMJ G> GMJ \N= KQFL9;LA; ;GEHD=PALQ E=9KMJ=K A= E=9F D=F?L@ G> 0MFAL ;D9MK= 9F< FGMF H@J9K= 9F< L@= KM:;D9MK= J9LAG
K@GO=< 9F GN=J9DD KA?FA>A;9FL =>>=;L >GJ HJG\;A=F;Q D=N=D O@=J=9K L@= ;GGJ<AF9LAGF J9LAG <A< FGL 1@= >9;L L@9L L@= E=9KMJ= G> KMHJ9
UNCORRECTED PROOF
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Fig. 6. $MAJ9M< K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H    H    H  
Fig. 7. %!! K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H    H    H  
Fig. 8. *1)! K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H    H    H  
;D9MK9D ;GEHD=PALQ A= E=9F D=F?L@ G> 0MFAL K@GO=< L@= @A?@=KL FME:=J G> KA?FA>A;9FL <A>>=J=F;=K :=LO==F HJG\;A=F;Q D=N=DK AK AF
DAF= OAL@ HJ=NAGMK KLM<A=K != D=J;I %GMK=F  $9F  &O9K@AL9 =L 9D  1@= KA?FA>A;9FL <A>>=J=F;=K :=LO==F HJG\
;A=F;Q D=N=DK O= >GMF< >GJ E=9F D=F?L@ G> FGMF H@J9K= 9F< LG 9 D=KK=J =PL=FL E=9F D=F?L@ G> ;D9MK= 9J= EGJ= MF=PH=;L=< != D=J;I
 %GMK=F  =N=F L@GM?@ AL K@GMD< := 9<<=< L@9L FGL E9FQ HJ=NAGMK KLM<A=K AF;DM<=< E=9KMJ=K G> ;D9MK9D 9F< H@J9K9D ;GEHD=PALQ
&F L@= HJ=K=FL KLM<Q E=9F D=F?L@ G> 0MFAL ;D9MK= 9F< FGMF H@J9K= FGL GFDQ J=KMDL=< AF 9F GN=J9DD KA?FA>A;9FL <A>>=J=F;= :=LO==F
HJG\;A=F;Q D=N=DK :ML L@=Q ;GMD< 9DKG <AKLAF?MAK@ :=LO==F LOG 9<B9;=FL D=N=DK D=N=DK 9F<  &F != D=J;I 9F< %GMK=F
UNCORRECTED PROOF
 B. Bulté and H. Roothooft / System xxx (xxxx) 102246
Fig. 9. * &N=J:K K;GJ=K H=J HJG\;A=F;Q D=N=D OAL@ KA?FA>A;9FL +,3 HGKL@G; H9AJOAK= <A>>=J=F;=K  H   H   H 
Table 4
-9J9E=L=J =KLAE9L=K >GJ GJ<AF9D DG?AKLA; J=?J=KKAGF
-9J9E=L=J "KLAE9L= 0L9F<9J<"JJGJ 0L9F<9J<AK=<=KLAE9L=β 49D< χHN9DM=
&FL=J;=HLK
   
   
   
   
0 /     
*)     
*)+-     
$    
*1)!     
* &     
 H    H    H   +9?=DC=JC=K /  ))  0GE=JK !  /, 
K  <9L9 E=9F D=F?L@ G> 0MFAL ;GMD< <AKLAF?MAK@ :=LO==F D=N=DK  9F<  G> L@= >GMJ HJG\;A=F;Q D=N=DK MK=< AF L@= KLM<Q :ML FGL
:=LO==F L@= L@AJ< 9F< L@= EGKL 9<N9F;=< D=N=D O@A;@ ;9F := ;GFKA<=J=< LG := KAEAD9J AF GMJ <9L9 O@=J= FGF= G> L@= E=9KMJ=K ;GMD<
<AKLAF?MAK@ :=LO==F L@= LOG @A?@=KL D=N=DK 1@= \F<AF? L@9L L@= KM:;D9MK= J9LAG ?9N= JAK= LG 9F GN=J9DD KA?FA>A;9FL <A>>=J=F;= :=LO==F
D=N=DK ;GF\JEK 0==<@GMK= =L 9DK  KLM<Q O@A;@ 9DKG MK=< &")10 KH=9CAF? L=KL <9L9 9F< AK 9DKG AF DAF= OAL@ GL@=J HJ=NAGMK KLM<A=K
!= D=J;I %GMK=F  (9F?  4@AD= 0==<@GMK= =L 9D  <A< FGL AFN=KLA?9L= :=LO==F O@A;@ D=N=DK L@= <A>>=J=F;=K ;GMD<
:= >GMF< GMJ H9AJOAK= ;GEH9JAKGFK K@GO L@9L =N=F L@GM?@ KM:GJ<AF9LAGF AF;J=9K=K DAF=9JDQ >JGE D=N=DK  LG  AL ;9FFGL <AK;JAEAF9L=
:=LO==F 9<B9;=FL D=N=DK
6.2. Which complexity measures correlate best with pro>ciency?
1@= J=KMDLK G> L@= GJ<AF9D DG?AKLA; J=?J=KKAGF 9J= FGN=D AF ;GEH9JAKGF LG L@= HJ=NAGMK KLM<A=K GF L@= J=D9LAGFK@AH :=LO==F ) KH==;@
;GEHD=PALQ 9F< ) HJG\;A=F;Q O@A;@ O= <=K;JA:=< 1@=Q K@GO L@9L GF= D=PA;9D $MAJ9M<K AF<=P GF= KQFL9;LA; KM:;D9MK= J9LAG 9F<
GF= EGJH@GDG?A;9D ;GEHD=PALQ E=9KMJ= EGJH@GDG?A;9D ;GEHD=PALQ AF<=P  N=J:K =E=J?=< 9K KA?FA>A;9FL HJ=<A;LGJK G> ) HJG\;A=F;Q
LG?=L@=J =PHD9AFAF? 9F =KLAE9L=< LOG L@AJ<K G> L@= N9JA9F;= AF HJG\;A=F;Q D=N=D 1@AK 9F9DQKAK AF<A;9L=K L@9L AL AK OGJL@O@AD= LG ;GE:AF=
<A>>=J=FL ;GEHD=PALQ <AE=FKAGFK 9F< E=9KMJ=K L9HHAF? AFLG N9JAGMK 9KH=;LK G> ;GEHD=PALQ O@=F L@= 9AE AK LG 9KK=KK ) HJG\;A=F;Q
$=F=J9DDQ KH=9CAF? $MAJ9M<K AF<=P G> D=PA;9D <AN=JKALQ =E=J?=< >JGE GMJ KLM<Q 9K L@= :=KL GN=J9DD HJ=<A;LGJ G> ) HJG\;A=F;Q DKG AF
3=JKHGGJ =L 9DK  KLM<Q G> ) OJALAF? $MAJ9M<K AF<=P O9K K@GOF LG := GF= G> L@= E=9KMJ=K L@9L ;GMD< <AK;JAEAF9L= :=KL :=LO==F
D=9JF=JK OAL@ <A>>=J=FL HJG\;A=F;Q D=N=DK 9F< L@AK 9;JGKK 9 OA<= J9F?= G> D=N=DK ,MJ <=L9AD=< :=LO==FD=N=D 9F9DQK=K >GJ L@= <A>>=J=FL
E=9KMJ=K 9DKG K@GO @GO=N=J L@9L L@= J=D9LAGFK@AH :=LO==F ;GEHD=PALQ E=9KMJ=K 9F< ) HJG\;A=F;Q AK FGL 9DO9QK DAF=9J 9F< L@9L
<A>>=J=FL E=9KMJ=K E9Q := EGJ= K=FKALAN= LG ;@9F?=K AF HJG\;A=F;Q 9L <A>>=J=FL HJG\;A=F;Q D=N=DK
6.3. Limitations
1@AK KLM<Q @9K 9 FME:=J G> DAEAL9LAGFK #AJKL L@= &")10 <9L9 O= MK=< 9J= FGL DGF?ALM<AF9D O@A;@ E=9FK O= ;GMD< GFDQ ;@9J
9;L=JAK= ) <=N=DGHE=FL9D H9LL=JFK AF :JG9< KLJGC=K 9L L@= ?JGMH D=N=D 9F< FGL E9C= 9FQ ;D9AEK 9:GML AF<ANA<M9D ) <=N=DGH
UNCORRECTED PROOF
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E=FL 1@AK AEHDA=K O= @9< LG <AKJ=?9J< AF<ANA<M9D N9JA9LAGF LG 9 D9J?= =PL=FL 9K O=DD 9K AF<ANA<M9D <=N=DGHE=FL9D H9LL=JFK O@A;@ @9N=
:==F K@GOF LG N9JQ ?J=9LDQ 9;JGKK D=9JF=JK MDLV  %GMK=F  3Q9LCAF9 =L 9D  0=;GF< FG ;GJJ=;LAGFK >GJ EMDLAHD= L=KLAF?
=? GF>=JJGFA O=J= 9HHDA=< LG L@= H9AJOAK= ;GEH9JAKGFK 9;;GEH9FQAF? L@= +,3K =N=F L@GM?@ L@AK AK G>L=F J=;GEE=F<=< #A=D<
 #MLMJ= KLM<A=K ;GMD< 9AE >GJ D9J?=J K9EHD= KAR=K H=J HJG\;A=F;Q D=N=D AF GJ<=J LG AF;J=9K= L@= KL9LAKLA;9D HGO=J G> L@= L=KLK &F
;J=9KAF? L@= K9EHD= KAR= OGMD< 9DKG := :=F=\;A9D >GJ L@= ?=F=J9DAK9:ADALQ G> L@= J=KMDLK 1@AJ< =N=F L@GM?@ L@= K;GJ= L=KL AF<A;9L=< L@9L
L@= HJGHGJLAGF9D G<<K 9KKMEHLAGF MF<=JDQAF? GMJ ;MEMD9LAN= DG?AL EG<=D O9K FGL NAGD9L=< KM;@ 9 EG<=D 9KKME=K =IM9D =>>=;LK G> <=
H=F<=FL N9JA9:D=K 9;JGKK <A>>=J=FL D=N=DK G> L@= AF<=H=F<=FL N9JA9:D= 1@= <=K;JAHLAN= KL9LAKLA;K AF<A;9L= L@9L KM;@ 9 EG<=D ;9FFGL >MDDQ
<G BMKLA;= LG L@= <AN=JK= H9LL=JFK G:K=JN=< >GJ L@= <A>>=J=FL ;GEHD=PALQ E=9KMJ=K #AF9DDQ HJG\;A=F;Q D=N=D AK GH=J9LAGF9DAK=< AF L@AK
KLM<Q 9K &")10 D=N=D O@A;@ AK <=L=JEAF=< GF L@= :9KAK G> KM:B=;LAN= J9LAF?K G> KH=9CAF? L9KCK AF;DM<AF? L@= EGFGDG?M=K L@9L ;GFKLALML=
GMJ <9L9K=L *GJ=GN=J L@= JM:JA;K MK=< >GJ L@= KM:B=;LAN= 9KK=KKE=FL G> HJG\;A=F;Q D=N=D AF;DM<= J=>=J=F;=K LG ;GEHD=PALQJ=D9L=< >9;
LGJK &L ;9FFGL := JMD=< GML L@9L 9L D=9KL H9JL G> L@= 9KKG;A9LAGF :=LO==F HJG\;A=F;Q D=N=D 9F< ;GEHD=PALQ K;GJ=K >GMF< AF L@AK KLM<Q AK
;9MK=< :Q L@AK ;GFF=;LAGF
7. Conclusions
1@= HJ=K=FL KLM<Q GF L@= J=D9LAGFK@AH :=LO==F FAF= ;GEHD=PALQ E=9KMJ=K 9F< \N= <A>>=J=FL D=N=DK G> GJ9D HJG\;A=F;Q 9K E=9KMJ=<
:Q L@= &")10 KH=9CAF? L=KL ;GF\JEK HJ=NAGMK KLM<A=K O@A;@ @9N= >GMF< L@9L D=9JF=JK 9L @A?@=J D=N=DK G> HJG\;A=F;Q L=F< LG HJG<M;=
EGJ= ;GEHD=P D9F?M9?= "N=F L@GM?@ O= >GMF< @A?@=J ;GEHD=PALQ K;GJ=K AF @A?@=J HJG\;A=F;Q D=N=DK >GJ E=9KMJ=K G> D=PA;9D KQFL9;LA;
9F< EGJH@GDG?A;9D ;GEHD=PALQ L@= G:K=JN=< H9LL=JFK <A>>=J KM:KL9FLA9DDQ 9;JGKK E=9KMJ=K &> O= GFDQ ;GFKA<=J <A>>=J=F;=K :=LO==F 9<
B9;=FL HJG\;A=F;Q D=N=DK O= G:K=JN=< 9 KA?FA>A;9FL AF;J=9K= AF EGJH@GDG?A;9D JA;@F=KK 9K E=9KMJ=< :Q L@= EGJH@GDG?A;9D ;GEHD=PALQ
AF<=P :=LO==F D=N=DK  9F<  AF D=PA;9D <AN=JKALQ $MAJ9M<K AF<=P :=LO==F D=N=DK  9F<  9F< AF GN=J9DD KQFL9;LA; E=9F D=F?L@ G>
0MFAL ;D9MK9D E=9F D=F?L@ G> ;D9MK= 9F< H@J9K9D ;GEHD=PALQ E=9F D=F?L@ G> FGMF H@J9K= 9K O=DD 9K D=PA;9D <AN=JKALQ $MAJ9M<K
AF<=P 9F< %!! :=LO==F D=N=DK  9F<  4= <A< FGL G:K=JN= KA?FA>A;9FL <A>>=J=F;=K AF ;GEHD=PALQ :=LO==F L@= @A?@=KL LOG HJG\;A=F;Q
D=N=DK AF GMJ <9L9K=L A=  9F<  &F 9<<ALAGF O= >GMF< L@9L L@= $MAJ9M< AF<=P L@= KM:;D9MK= J9LAG 9F< L@= EGJH@GDG?A;9D ;GEHD=PALQ
AF<=P 9HHDA=< LG N=J:K O=J= KA?FA>A;9FL HJ=<A;LGJK >GJ HJG\;A=F;Q D=N=D AF GMJ GJ<AF9D DG?AKLA; J=?J=KKAGF EG<=D =PHD9AFAF? 9JGMF< LOG
L@AJ<K G> L@= N9JA9F;= AF HJG\;A=F;Q D=N=D
4AL@ L@AK KLM<Q O= <A< FGL AFL=F< LG E9C= ;D9AEK 9:GML L@= AF@=J=FL N9DM= GJ N9DA<ALQ G> ;GEHD=PALQ E=9KMJ=K 9K E=9KMJ=K G>
;GEHD=PALQ /9L@=J GMJ 9AE O9K LG \F< GML O@A;@ ;GEHD=PALQ E=9KMJ=K K@GO KA?FA>A;9FL <A>>=J=F;=K :=LO==F D=9JF=JK OAL@ <A>>=J=FL
HJG\;A=F;Q D=N=DK GJ AF GL@=J OGJ<K O@A;@ E=9KMJ=K 9J= HGL=FLA9DDQ ?GG< AF<A;9LGJK G> ) HJG\;A=F;Q 9F< HGL=FLA9DDQ ) <=N=DGH
E=FL &F L@AK K=FK= GMJ J=KMDLK 9J= AF>GJE9LAN= >GJ >MLMJ= KLM<A=K MKAF? ;GEHD=PALQ E=9KMJ=K 9K G:B=;LAN= AF<A;9LGJK G> ) D=9JF=J
HJG\;A=F;Q 1@=Q 9DKG @9N= AEHDA;9LAGFK >GJ D9F?M9?= L=KLAF? =N=F L@GM?@ L@= D9:GMJAFL=FKAN=F=KK G> LJ9FK;JA:AF? 9F< ;G<AF? GJ9D
<9L9 9J= 9F G:KL9;D= LG 9MLGE9L=< 9F9DQK=K KAF;= ;MJJ=FL 9MLGE9L=< ;GEHD=PALQ LGGDK 9J= ?=9J=< LGO9J<K L@= 9F9DQKAK G> OJALL=F D9F
?M9?= GJ L@GJGM?@DQ ;D=9F=< MH 9F< ;9J=>MDDQ LJ9FK;JA:=< N=JKAGFK G> GJ9D <9L9 +=N=JL@=D=KK G:B=;LAN= ;GEHD=PALQ 9F9DQK=K ;9F := 9
MK=>MD 9<<ALAGF LG KM:B=;LAN= HJG\;A=F;Q J9LAF?K 9DKG >GJ D9F?M9?= L=KLAF? HMJHGK=K
Funding
1@AK J=K=9J;@ <A< FGL J=;=AN= 9FQ KH=;A\; ?J9FL >JGE >MF<AF? 9?=F;A=K AF L@= HM:DA; ;GEE=J;A9D GJ FGL>GJHJG\L K=;LGJK
CRediT authorship contribution statement
Bram Bulté: GF;=HLM9DAR9LAGF *=L@G<GDG?Q 0G>LO9J= #GJE9D 9F9DQKAK Hanne Roothooft: GF;=HLM9DAR9LAGF #GJE9D 9F9DQKAK
&FN=KLA?9LAGF /=KGMJ;=K !9L9 ;MJ9LAGF
Acknowledgements
1@AK H9H=J J=HGJLK GF J=K=9J;@ MKAF? <9L9 HJGNA<=< :Q 9E:JA<?= "F?DAK@ )9F?M9?= KK=KKE=FL
Appendix D. Supplementary data
0MHHD=E=FL9JQ <9L9 LG L@AK 9JLA;D= ;9F := >GMF< GFDAF= 9L @LLHK<GAGJ?BKQKL=E
Appendix A. Descriptive statistics
Table A.1
!=K;JAHLAN= KL9LAKLA;K E=9FK OAL@ KL9F<9J< <=NA9LAGFK :=LO==F :J9;C=LK
-JG\;A=F;QD=N=D
F  
F  
F  
F  
F  
1GL9D
F  
0QFL9;LA;;GEHD=PALQ
UNCORRECTED PROOF
 B. Bulté and H. Roothooft / System xxx (xxxx) 102246
Mean length of AS-unit 











Subclause ratio 











Mean length of clause 











Coordination ratio 











Mean length of NP 











Lexical complexity
Guiraud's index 











HD-D 











MTLD 











Morphological complexity
MCI 











Appendix B. ANOVAs
Table B.1
/=KMDLK +,3K
# H "_=;LKAR==L9
0QFL9;LA;;GEHD=PALQ
Mean length of AS-unit   
Subclause ratio   
Mean length of clause   
Coordination ratio   
Mean length of NP   
Lexical complexity
Guiraud's index   
HD-D   
MTLD   
Morphological complexity
MCI   
Appendix C. Correlations between complexity measures
Table C.1
-=9JKGF ;GJJ=D9LAGFK :=LO==F ;GEHD=PALQ E=9KMJ=K  H    H    H  
0 / *) / *)+- * & $ %!! *1)!
*)0        
0 /       
*)      
/     
*)+-    
* &   
$  
%!! 
References
::9K (@MK@AC $  %M@L9   &FN=KLA?9LAF? KQFL9;LA; ;GEHD=PALQ AF "#) D=9JF=JKOJALAF? 9;JGKK ;GEEGF "MJGH=9F >J9E=OGJC G> J=>=J=F;= D=N=DK   9F<
 HHDA=< )AF?MAKLA;K <GA9HHDAF9EQ 9EQ
?J=KLA   F9DQKAK G> GJ<AF9D ;9L=?GJA;9D <9L9 F< =< +=O 6GJC 4AD=Q
A:=J !  39JA9LAGF 9;JGKK KH==;@ 9F< OJALAF? 9E:JA<?= 9E:JA<?= 2FAN=JKALQ -J=KK
A:=J ! $J9Q   -GGFHGF (  0@GMD< O= MK= ;@9J9;L=JAKLA;K G> ;GFN=JK9LAGF LG E=9KMJ= ?J9EE9LA;9D ;GEHD=PALQ AF ) OJALAF? <=N=DGHE=FL 1=KGD .M9JL=JDQ
 
A:=J ! $J9Q   0L9HD=K 0  -J=<A;LAF? H9LL=JFK G> ?J9EE9LA;9D ;GEHD=PALQ 9;JGKK D9F?M9?= =P9E L9KC LQH=K 9F< HJG\;A=F;Q D=N=DK HHDA=< )AF?MAKLA;K 

J=RAF9 3  -9DDGLLA $  *GJH@GDG?A;9D ;GEHD=PALQ AF OJALL=F ) L=PLK 0=;GF< )9F?M9?= /=K=9J;@  
UNCORRECTED PROOF
B. Bulté and H. Roothooft / System xxx (xxxx) 102246 
MDLV   %GMK=F   !=\FAF? 9F< GH=J9LAGF9DAKAF? ) ;GEHD=PALQ &F %GMK=F  (MAC=F #  3=<<=J & "<K !AE=FKAGFK G> ) H=J>GJE9F;= 9F< HJG\;A=F;Q
&FN=KLA?9LAF? ;GEHD=PALQ 9;;MJ9;Q 9F< ]M=F;Q AF 0) HH  EKL=J<9E 'G@F =FB9EAFK
MDLV   %GMK=F   GF;=HLM9DARAF? 9F< E=9KMJAF? K@GJLL=JE ;@9F?=K AF ) OJALAF? ;GEHD=PALQ 'GMJF9D G> 0=;GF< )9F?M9?= 4JALAF?  
<GABBKDO
MDLV   %GMK=F   0QFL9;LA; ;GEHD=PALQ AF ) OJALAF? &F<ANA<M9D H9L@O9QK 9F< =E=J?AF? ?JGMH LJ=F<K &FL=JF9LAGF9D 'GMJF9D G> HHDA=< )AF?MAKLA;K 
 <GAAB9D
MDLV  %GMK=F  -A=JJ9J< *  39F !9=D= 0  &FN=KLA?9LAF? D=PA;9D HJG\;A=F;Q <=N=DGHE=FL GN=J LAE= L@= ;9K= G> !ML;@KH=9CAF? D=9JF=JK G> #J=F;@ AF
JMKK=DK 'GMJF9D G> #J=F;@ )9F?M9?= 0LM<A=K   <GA0
GFFGJ)AFLGF ' -GDAG  GEH9JAF? H=JKH=;LAN=K GF ) OJALAF? *MDLAHD= 9F9DQK=K G> 9 ;GEEGF ;GJHMK 'GMJF9D G> 0=;GF< )9F?M9?= 4JALAF?  
JGKL@O9AL= -  DGF?ALM<AF9D EMDLA<AE=FKAGF9D 9F9DQKAK G> "- OJALAF? !=L=JEAFAF? "- ;GMJK= =_=;LAN=F=KK 'GMJF9D G> "F?DAK@ >GJ ;9<=EA; -MJHGK=K 

!= D=J;I  1@= <=N=DGHE=FL G> D=PA;9D ;GEHD=PALQ AF K=;GF< D9F?M9?= 9;IMAKALAGF ;JGKKDAF?MAKLA; KLM<Q G> ) #J=F;@ 9F< "F?DAK@ "2/,0) 6=9J:GGC 

!= D=J;I  %GMK=F  ;JGKKDAF?MAKLA; H=JKH=;LAN= GF KQFL9;LA; ;GEHD=PALQ AF ) <=N=DGHE=FL 0QFL9;LA; =D9:GJ9LAGF 9F< <AN=JKALQ 1@= *G<=JF )9F?M9?=
'GMJF9D  
!= D=J;I  %GMK=F  1@= <=N=DGHE=FL G> EGJH@GDG?A;9D ;GEHD=PALQ ;JGKKDAF?MAKLA; KLM<Q G> ) #J=F;@ 9F< "F?DAK@ 0=;GF< )9F?M9?= /=K=9J;@ 

!=JJ /  ,J<AF9D J=KHGFK= EG<=DAF? OAL@ L@= ),$&01& HJG;=<MJ= -JG;==<AF?K G> L@= 00 ?DG:9D >GJME  ;GF>=J=F;= 9JQ +  00 &FKLALML= &F;
"DDAK /  9JC@MAR=F $ -  F9DQKAF? D=9JF=J D9F?M9?= ,P>GJ< ,P>GJ< 2FAN=JKALQ -J=KK
#A=D<   !AK;GN=JAF? KL9LAKLA;K MKAF? 0-00 J< =< )GF<GF 09?=
#GKL=J - 1GFCQF   4A??D=KOGJL@ $  *=9KMJAF? KHGC=F D9F?M9?=  MFAL >GJ 9DD J=9KGFK HHDA=< )AF?MAKLA;K  
#JA?AF9D "  4=A?D= 0  "PHDGJAF? EMDLAHD= HJG\D=K G> ) OJALAF? MKAF? EMDLA<AE=FKAGF9D 9F9DQKAK 'GMJF9D G> 0=;GF< )9F?M9?= 4JALAF?  
$9F 7  GEHD=PALQ E=9KMJ=K L9KC LQH= 9F< 9F9DQLA; =N9DM9LAGFK G> KH=9CAF? HJG\;A=F;Q AF 9 K;@GGD:9K=< 9KK=KKE=FL ;GFL=PL )9F?M9?= KK=KKE=FL .M9JL=JDQ
 
$MAJ9M< -  -JG:DWE=K =L EVL@G<=K <= D9 KL9LAKLAIM= DAF?MAKLAIM= !GJ<J=;@L /=A<=D
$QDDKL9< % $J9F>=D<L ' =JF9J<AFA - (UDDCNAKL *  )AF?MAKLA; ;GJJ=D9L=K LG ;GEEMFA;9LAN= HJG\;A=F;Q D=N=DK G> L@= "#/ 1@= ;9K= G> KQFL9;LA; ;GEHD=PALQ
AF OJALL=F ) "F?DAK@ ) #J=F;@ 9F< ) &L9DA9F "2/,0) 6=9J:GGC  
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... Although this index, commonly referred to as Root TTR or Guiraud's index, gained a reputation as an appropriate substitute for TTR and is still used fairly widely (Bulté & Housen, 2019;Lambelet, 2021), studies have repeatedly shown that it strongly overcorrects TTR's negative relationship with text length (e.g., Koizumi & In'nami, 2012;McCarthy & Jarvis, 2010;Zenker & Kyle, 2021). One possible reason for the durability of Root TTR in the field is that it tends to demonstrate a relatively strong relationship with proficiency, and it is certainly an improvement over TTR because it is positively correlated with text length and therefore does not penalize longer essays (see Bulté & Roothooft, 2020;Treffers-Daller et al., 2018). However, because the index is intrinsically positively correlated with text length, it is unclear to what degree increases in Root TTR scores can be attributed to increases in lexical diversity, fluency, productivity, and/or topic development, among other potential causes for increases in text length. ...
... The default solution has been to average scores (including partial factors) for MTLD calculated forward and backward through the text, though windowed approaches have also been used (see Vidal & Jarvis, 2020;Zenker & Kyle, 2021). Use of MTLD is increasingly common in SLA studies (e.g., Bulté & Roothooft, 2020;Pfenniger, 2020;Vidal & Jarvis, 2020). ...
... Studies have taken two major approaches in providing validity evidence for lexical diversity indices. In the first (and most common) approach, relationships between lexical diversity scores and proficiency scores (broadly construed) are used (Bulté & Roothooft, 2020;Engber, 1995;Jarvis, 2002;Koizumi et al., 2022;Treffers-Daller et al., 2018;Zenker & Kyle, 2021). For example, Engber (1995) investigated the relationship between lexical variety index scores (both including and excluding lexical errors) and holistic judgments of essay quality (n = 66). ...
Article
Although lexical diversity is often used as a measure of productive proficiency (e.g., as an aspect of lexical complexity) in SLA studies involving oral tasks, relatively little research has been conducted to support the reliability and/or validity of these indices in spoken contexts. Furthermore, SLA researchers commonly use indices of lexical diversity such as Root TTR (Guiraud’s index) and D (vocd-D and HD-D) that have been preliminarily shown to lack reliability in spoken L2 contexts and/or have been consistently shown to lack reliability in written L2 contexts. In this study, we empirically evaluate lexical diversity indices with respect to two aspects of reliability (text-length independence and across-task stability) and one aspect of validity (relationship with proficiency scores). The results indicated that neither Root TTR nor D is reliable across different text lengths. However, support for the reliability and validity of optimized versions of MATTR and MTLD was found.
... Introduction into the relationships between linguistic complexity and L2 proficiency or L2 writing quality (Lu, 2011;Kyle andCrossley, 2017, 2018;Brezina and Pallotti, 2019;Khushik and Huhta, 2019;Bulté and Roothooft, 2020;Ouyang et al., 2022;Zhang and Lu, 2022). In this line of research, a primary concern lies in identifying valid and reliable complexity metrics that can effectively predict different L2 learners' proficiency levels or developmental stages (Egbert, 2017;Lu, 2017). ...
... More recent studies have addressed the need for fine-grained syntactic complexity metrics and assessed their abilities in predicting the quality of written or spoken production (Kyle andCrossley, 2017, 2018). Concerning lexical metrics, lexical diversity metrics such as Guiraud's index, type-token ratio (Kettunen, 2014;De Clercq, 2015;Treffers-Daller et al., 2016;Bulté and Roothooft, 2020) and newly proposed lexical sophistication metrics such as n-gram association strength (Kim et al., 2017; have proved to be effective in capturing differences associated with L2 proficiency. ...
... To further elaborate learners' L2 performance in SLA research, Bulté and Housen (2012) distinguished the broader notion of absolute complexity into propositional complexity, discourse-interactional complexity, and linguistic complexity. What we focus on in the present study is the linguistic complexity that denotes an absolute, objective, and essentially quantitative property of language units, features, and (sub)systems (Bulté and Roothooft, 2020). More precisely, we adopted the Kolmogorov complexity, which is defined as the length of the shortest description that can reproduce the sample text (Li et al., 2004;Juola, 2008). ...
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Based on 774 argumentative writings produced by Chinese English as a foreign language (EFL) learners, this study examined the extent to which Kolmogorov complexity metrics can distinguish the proficiency levels of beginner, lower-intermediate, and upper-intermediate second language (L2) English learners. Kolmogorov complexity metric is a holistic information-theoretic approach, which measures three facets of linguistic complexity, i.e., overall, syntactic, and morphological complexity simultaneously. To assess its validity in distinguishing L2 proficiency, Kolmogorov complexity metric is compared with traditional syntactic and morphological complexity metrics as well as fine-grained syntactic complexity metrics. Results showed that Kolmogorov overall and syntactic complexity could significantly distinguish any adjacent pair of L2 levels, serving as the best separators explored in the present study. Neither Kolmogorov morphological complexity nor other complexity metrics at both the syntactic and morphological levels can distinguish between all pairs of adjacent levels. Results of correlation analysis showed that Kolmogorov syntactic complexity was not or weakly correlated with all the fine-grained syntactic complexity metrics, indicating that they may address distinct linguistic features and can complement each other to better predict different proficiency levels.
... In the literature pertaining to CAF, complexity is generally assessed through the competence to use a wide and varied range of advanced vocabulary and sophisticated structures in the target language (Skehan, 1998;Ellis, 2003Ellis, , 2008Housen et al., 2012). Because of its polysemous nature, complexity in language learning retains multiple meanings (Michel, 2017;Bulté and Roothooft, 2020) and is the most debated construct of the CAF triad (Pallotti, 2009). Following Michel (2017), complexity can be applied to three different dimensions, i.e., developmental, cognitive and linguistic complexity. ...
... In literature, a considerable number of EFL studies have investigated the role of lexical complexity in language learning, but most of their data were written English (e.g., Barrot and Gabinete, 2021;Han et al., 2021). In contrast, few studies have investigated oral lexical complexity in the context of EFL learning (Bulté and Roothooft, 2020). In response, the present study seeks to address this gap by examining EFL learners' lexical complexity in their oral English. ...
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Although the automatic speech recognition (ASR) technology is increasingly used for commercial purposes, its impact on language learning has not been extensively studied. The present work examined the effects of leveraging ASR technology to support English vocabulary learning in a tertiary flipped setting. A control group and an experimental group of college students participated in this 14-week study. Both groups had their English classes in a flipped fashion, but the experimental group was assigned ASR-assisted oral tasks for pre-class self-learning. The pre- and post-intervention in-class task performance of both groups was audio-recorded and transcribed for data analysis. The triadic complexity-accuracy-fluency (CAF) framework was adopted to evaluate the participants’ vocabulary learning. The between- and within-subjects effects were examined mainly through procedures of MANCOVA and mixed-design repeated measures ANCOVA. Results showed that on all the metrics of lexical complexity and speed fluency, the experimental group outperformed the control group, and had significant growth over time. On the other hand, the control group only improved significantly overtime on the G-index. On lexical accuracy, there was no significant difference between the two groups, and the within-subjects effect was not significant for either group. The findings lent some support to Skehan’s Trade-off Hypothesis and discussions were conducted regarding the triarchic CAF framework.
... The construct of proficiency was also assessed from a multi-componential perspective using Following the recommendations of Norris and Ortega (2009), complexity was measured at three levels: global, subordinate, and subclausal levels. Complexity at the global level was operationalized as mean length of AS-unit (total number of words by the total number of AS-units), following Michel, Kuiken, and Vedder (2007) and Bulté and Roothooft (2020). Complexity at the subordinate level was operationalized as the total number of subordinate clauses divided by the total number of AS-units, as in De Clercq and Housen (2017). ...
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This study sought to investigate linguistic gains and crosslinguistic influence (CLI) from English and Spanish on the oral production of postsecondary L3 Portuguese learners, comparing the effects of two pedagogical approaches: oral synchronous telecollaboration between Portuguese learners and native speakers (Teletandem), and group work among learners in the L2 classroom. Participants met weekly for eight weeks, after which gains in oral proficiency were measured using an Elicited Imitation Task (EIT) and a listening comprehension test (LCT). Linguistic development was also measured by various indices of oral complexity, accuracy, and fluency (CAF). Results showed significant improvement in proficiency and all CAF measures over time, but no differences between groups. Spanish CLI was significantly higher than English CLI for both groups and the only type of CLI to significantly decrease. Participants' perceptions and beliefs, and the lack of differential performance across groups is discussed, considering different pedagogical and theoretical approaches to telecollaboration.
... As a central construct in second language (L2) research, syntactic complexity, over the past few decades, has been increasingly investigated in relation to L2 proficiency (e.g. Ai & Lu, 2013;Bulté & Roothooft, 2020;Ortega, 2003;Vyatkina, 2013), L2 devel-opment (e.g. Bulté & Housen, 2018;De Clercq & Housen, 2017;Spoelman & Verspoor, 2010), and L2 writing quality (e.g. ...
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Automated tools for syntactic complexity measurement are increasingly used for analyzing various kinds of second language corpora, even though these tools were originally developed and tested for texts produced by advanced learners. This study investigates the reliability of automated complexity measurement for beginner and lower-intermediate L2 English data by comparing manual and automated analyses of a corpus of 80 texts written by Dutch-speaking learners. Our quantitative and qualitative analyses reveal that the reliability of automated complexity measurement is substantially affected by learner errors, parser errors, and Tregex pattern undergeneration. We also demonstrate the importance of aligning the definitions of analytical units between the computational tool and human annotators. In order to enhance the reliability of automated analyses, it is recommended that certain modifications are made to the system, and non-advanced L2 English data are preprocessed prior to automated analyses.
... TAALED (The Tool for the Academic Analysis of Lexical Diversity) is used in calculating the lexical density of a corpus for types and tokens and eight indices of lexical diversity (Kyle, 2018). Studies of Bulté and Roothooft (2020) and Skalicky et al. (2020) are recent examples of the use of TAALED for lexical diversity analysis. ...
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... Defining L2 proficiency is part of explaining individual differences in the attainment of an L2 (Hulstijn, 2011). L2 proficiency can be defined as the overall level of development of an L2 learner, meaning how well the learners know a language, or how well they are able to use the language in various communicative situations, in a given modality (Bulté & Roothooft, 2020;Hulstijn, 2011). A variety of models have been proposed to describe the notion of L2 proficiency. ...
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The creation of the Common European Framework of Reference for Languages (CEFR) has given rise to interest and debate among policy makers, testers, teachers and researchers alike in the reliability and feasibility of the assessment of second language (L2) proficiency. This volume brings together concrete ideas on identifying and measuring L2 proficiency from different branches of SLA research (psycholinguistic, sociolinguistic, corpus-based, applied linguistics) to contribute to a deeper understanding of what it means to be proficient in an L2. The chapters introduce a wide range of tools that are innovative, reliable, and easy-to-use for the evaluation of learners' language level with respect to both productive and receptive skills and provide a variety of answers to the question of how to assess L2 proficiency in a valid, reliable and practical manner. The collection will therefore inspire language teachers, teacher trainers and language testing specialists and help them adapt their assessment practices when necessary, and will also be a valuable resource for postgraduate students and researchers.
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Syntactic complexity, along with accuracy and fluency, has been proposed as an essential construct in the description of second language proficiency. This study examined three dimensions of complexity using oral data from learners of German at the intermediate, advanced, and superior proficiency levels. The data were examined for complexity by subordination, complexity by coordination, and phrasal complexity. The results showed that all three complexity measures showed different patterns of use as proficiency level rises, which supports the understanding of complexity as a multi-dimensional construct. The results also showed that mean clause length was the most useful measure for distinguishing between adjacent proficiency levels. Neben Korrektheit und Flüssigkeit ist syntaktische Komplexität ebenfalls von zentraler Bedeutung für einige Modelle des Fremdsprachenerwerbsprozesses. Der vorliegende Beitrag untersucht drei verschiedene Komponenten der Komplexität in der Sprachproduktion von DaF-Lernenden unterschiedlicher Sprachniveaus. Drei Aspekte der Komplexität wurden in der Sprachproduktion untersucht: Koordination, Subordination, und Satzgliedlänge. Variiert haben sich alle drei Maße der Komplexität bei steigender Sprachkompetenz; die Ergebnisse unterstützen daher eine multidimensionale Konzeption von Komplexität. Am meisten haben sich die Sprachniveaus voneinander unterschieden im Bezug auf die Durchschnittssatzgliedlänge (mean length of clause), die sich als nützlich für die Unterscheidung der Sprachniveaus erwiesen hat.