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DOI: 10.1542/peds.2005-1316
2006;117;771Pediatrics
and Patrick H. Casey
C. Bernbaum, Charles R. Bauer, Camilia Martin, Elizabeth R. Woods, Anne Martin
JudyJennifer Yu, Mikhail Salganik, David T. Scott, Forrest C. Bennett, Libby L. Kay,
Marie C. McCormick, Jeanne Brooks-Gunn, Stephen L. Buka, Julie Goldman,
of Age for the Infant Health and Development Program
Early Intervention in Low Birth Weight Premature Infants: Results at 18 Years
http://pediatrics.aappublications.org/content/117/3/771.full.html
located on the World Wide Web at:
The online version of this article, along with updated information and services, is
of Pediatrics. All rights reserved. Print ISSN: 0031-4005. Online ISSN: 1098-4275.
Boulevard, Elk Grove Village, Illinois, 60007. Copyright © 2006 by the American Academy
published, and trademarked by the American Academy of Pediatrics, 141 Northwest Point
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ARTICLE
Early Intervention in Low Birth Weight Premature
Infants: Results at 18 Years of Age for the Infant
Health and Development Program
Marie C. McCormick, MD, ScD
a
, Jeanne Brooks-Gunn, PhD
b
, Stephen L. Buka, ScD, MS
a
, Julie Goldman, MSSA, MS
a
, Jennifer Yu, ScD, EdM
a
,
Mikhail Salganik, PhD
c
, David T. Scott, PhD
d
, Forrest C. Bennett, MD
e
, Libby L. Kay, MSSW, LCSW
f
, Judy C. Bernbaum, MD
g
,
Charles R. Bauer, MD
h
, Camilia Martin, MD, MS
i
, Elizabeth R. Woods, MD, MPH
j
, Anne Martin, DrPH, MPH
b
, Patrick H. Casey, MD
k
Departments of
a
Society, Human Development and Health, and
c
Biostatistics, Harvard School of Public Health, Boston, Massachusetts;
b
National Center for Children and
Families, Teachers College, and College of Physicians and Surgeons, Columbia University, New York, New York; Departments of
d
Psychiatry and Behavioral Sciences and
e
Pediatrics, University of Washington, Seattle, Washington;
f
Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas;
g
Department of
Pediatrics, University of Pennsylvania School of Medicine, Children’s Hospital of Philadelphia, Philadelphia, Pennsylvania;
h
Department of Pediatrics, University of Miami
School of Medicine, Miami, Florida;
i
Department of Neonatology, Beth Israel Deaconess Medical Center, Boston, Massachusetts;
j
Children’s Hospital Boston, Boston,
Massachusetts;
k
Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas
The authors have indicated they have no financial relationships relevant to this article to disclose.
ABSTRACT
OBJECTIVE. To assess whether improvements in cognitive and behavioral develop-
ment seen in preschool educational programs persist, we compared those in a
multisite randomized trial of such a program over the first 3 years of life (INT) to
those with follow-up only (FUO) at 18 months of age.
METHODS. This was a prospective follow-up of the Infant Health and Development
Program at 8 sites heterogeneous for sociodemographic characteristics. Originally
985 children were randomized to the INT (n ⫽ 377) or FUO (n ⫽ 608) groups
within 2 birth weight strata: heavier low birth weight (HLBW; 2001–2499 g) and
lighter low birth weight (LLBW; ⱕ2000 g). Primary outcome measures were the
Peabody Picture Vocabulary Test (PPVT-III), reading and mathematics subscales of
the Woodcock-Johnson Tests of Achievement, youth self-report on the Total
Behavior Problem Index, and high-risk behaviors on the Youth Risk Behavior
Surveillance System (YRBSS). Secondary outcomes included Weschler full-scale
IQ, caregiver report on the Total Behavior Problem Index, and caregiver and youth
self-reported physical health using the Medical Outcome Study measure. Assessors
were masked as to study status.
RESULTS. We assessed 636 youths at 18 years (64.6% of the 985, 72% of whom had
not died or refused at prior assessments). After adjusting for cohort attrition,
differences favoring the INT group were seen on the Woodcock-Johnson Tests of
Achievement in math (5.1 points), YRBSS (⫺0.7 points), and the PPVT-III (3.8
points) in the HLBW youth. In the LLBW youth, the Woodcock-Johnson Tests of
Achievement in reading was higher in the FUO than INT group (4.2).
CONCLUSIONS. The findings in the HLBW INT group provide support for preschool
education to make long-term changes in a diverse group of children who are at
developmental risk. The lack of observable benefit in the LLBW group raises
questions about the biological and educational factors that foster or inhibit sus-
tained effects of early educational intervention.
www.pediatrics.org/cgi/doi/10.1542/
peds.2005-1316
doi:10.1542/peds.2005-1316
Key Words
early intervention, long-term results, low
birth weight, randomized controlled trial
Abbreviations
IHDP—Infant Health and Development
Program
LLBW—lighter low birth weight
HLBW— heavier low birth weight
INT—intervention
FUO—follow-up only
YRBSS—Youth Risk Behavior Surveillance
System
BPI—Behavior Problem Index
WASI—Weschler Abbreviated Scale of
Intelligence
PPVT-III—Peabody Picture Vocabulary
Test-Version III
HSG— high school graduate
CI— confidence interval
LBW—low birth weight
Accepted for publication Aug 12, 2005
Address correspondence to Marie C.
McCormick, MD, ScD, Department of Society,
Human Development and Health, Harvard
School of Public Health, 677 Huntington Ave,
Boston, MA 02115. E-mail: mmccormi@hsph.
harvard.edu
PEDIATRICS (ISSN Numbers: Print, 0031-4005;
Online, 1098-4275). Copyright © 2006 by the
American Academy of Pediatrics
PEDIATRICS Volume 117, Number 3, March 2006 771
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I
NTENSIVE EARLY EDUCATIONAL interventions have
been documented to improve the cognitive outcomes
1
and, in some cases, reduce antisocial behavior early in
the school experience.
2
In several single-site, random-
ized studies of center-based interventions, longer-term
follow-up into adolescence and early adulthood has re-
vealed persistence of early-intervention effects seen as
greater school achievement,
3,4
less grade retention and
special education,
3,5
and more high school completion
6
and participation in college.
4
In addition to better edu-
cational outcomes, early-intervention programs have
also resulted in better social outcomes such as less ado-
lescent parenting
4
and less delinquency and fewer ar-
rests.
6–8
Parallel effects have been seen in follow-up of at
least 1 home-visiting program
9
and a nonrandomized
program conducted in several centers in 1 city, the Chi-
cago Child-Parent Center Program.
10
However, all of
these studies involve healthy, low-income, poor chil-
dren generally from a single site. Thus, inferences about
the generalizability of these results to groups more het-
erogeneous for socioeconomic status and health are lim-
ited.
The Infant Health and Development Program (IHDP)
was a multisite, randomized, controlled trial of an edu-
cational intervention until 3 years of age for low birth
weight (LBW) preterm infants. Infants were sampled
from 2 birth weight strata (ⱕ2000 g and 2001–2500 g) to
assure an oversample of those at higher developmental
risk (the lighter LBW [LLBW] group) and continuity
with studies of poor, normal birth weight children (the
heavier LBW [HLBW] group) at 8 sites, and as a result,
the sample for this study is quite heterogeneous for
socioeconomic status and health status, particularly neu-
rologic factors that might influence school outcomes.
The intervention consisted of home visits every week for
the first year and every other week in the second and
third year, daily center-based education beginning at 12
months corrected for duration of gestation continuing
until 36 months of age, with the addition of parent
support groups. All of the children received intensive
pediatric follow-up care. The program has been de-
scribed in detail elsewhere.
11–13
The results of the trial through 8 years of age have
been published previously
14–17
and will be summarized
briefly here. The assessment of outcomes was conducted
in 3 prior phases. At 36 months of age corrected for
duration of gestation, at the end of phase I (the trial
phase), the IQs of those who received the intervention
(INT) were substantially higher than those who received
follow-up services only (FUO): a 14-point difference for
the HLBW group and 7 points for the LLBW group.
Likewise, lower behavior problem scores were seen in
the INT group. By age 5 (phase II, the preschool period)
and age 8 (phase III, the early school period), no differ-
ences in behavior scores were observed. At both ages 5
and 8, the INT in the HLBW group still experienced a
significant advantage in IQ scores (4 points higher), as
well as mathematics achievement testing (4 points
higher). No differences in IQ or achievement between
INT and FUO groups were seen for the children in the
LLBW group.
The IHDP is based on the design and curriculum of
the Abecedarian Project,
18
and the results in IQ scores
and achievement testing parallel results seen in the
Abecedarian Project
18
at 8 years of age. More recent data
from that project reveal persisting differences in IQ and
achievement up to 21 years of age,
19
prompting us to
extend the follow-up of the IHDP to 18 years with a
fourth wave of data collection (phase IV). The purpose of
this effort is to ascertain whether such persistent differ-
ences would be observed in the IHDP, especially in the
HLBW group. In line with other studies of normal birth
weight children, we hypothesized that we would see
persistent IQ and achievement differences and less risky
behavior favoring the INT group.
METHODS
Study Population
Detailed information on the recruitment of the study
population and follow-up through 8 years of age has
been published previously
11–17,19
and will be summarized
briefly. To be eligible for the trial, an infant must have
been born in 1 of the participating hospitals at each of
the 8 sites at a birth weight ⱕ2500 g, a gestational age of
ⱕ37 weeks, and reside in a catchment area defined by
distance from the early educational center. Infants were
enrolled between October 1984 and August 1985 in 2
birth weight strata: ⱕ2000 g, and 2001–2500 g. Within
birth weight strata, infants were randomly assigned to
the INT group (n ⫽ 377) or FUO group (n ⫽ 608).
Although the sites were heterogeneous for a variety of
characteristics, the randomization procedure resulted in
comparability between the INT and FUO groups at study
entry.
14
Infants in both arms of the study received periodic
medical, developmental, and social service assessments
with referral for community services when indicated.
Those in the INT group received an educational program
delivered through home visits (weekly during the first
year and every other week during the second and third
years of life), a daily center-based program beginning at
12 months corrected for duration of gestation, and par-
ent support groups coinciding with the start of the cen-
ter-based program.
11
These parent support groups met
every other month. At the end of the INT period at 3
years of age, the children received whatever community
education programs were available at the site. Although
the availability of such services varied greatly among the
sites, there were no differences between the INT and
FUO groups in receipt of such services.
15
As noted above,
major assessment points for the intervention occurred at
3, 5, and 8 years of age. Completion rates at these ages
772 MCCORMICK, et al
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were 92%, 82%, and 89%, respectively. The lower rate
at age 5 reflects the lack of funding for staff to assess
children who were not close to any study site.
Data Collection at 18 Years of Age (Phase IV)
Measures
The phase IV assessment at 18 years of age was designed
to obtain information in the areas of academic achieve-
ment, behavior, cognitive abilities, and physical health.
To the extent possible, instruments were selected to
provide continuity with previous assessment periods and
to have known references or to have been used in large
population studies.
Academic Achievement
Academic achievement was assessed using the Wood-
cock-Johnson Tests of Achievement-Revised.
20
These
tests yielded letter-word identification, passage compre-
hension, calculation, and applied problems subtests of
the standard scores. Two scores were calculated, the
Woodcock-Johnson Tests of Achievement in reading
and in mathematics, referenced to a mean of 100 and an
SD of 15, with higher scores indicative of better achieve-
ment.
In addition, the youth’s mother or other caregiver
was asked about his/her progress in school. Specifically,
these questions deal with completion of school, grade
repetition, classification for special education, and school
dropout.
Behavior
Two aspects of behavior were assessed: risk behaviors
and more general behavioral problems. Risk behaviors
were assessed using youth self-report on questions taken
from the Youth Risk Behavior Surveillance System
(YRBSS).
21
Items from this survey were selected to char-
acterize the youth along dimensions affected by early
intervention in early studies: conduct problems, suicidal
ideation/attempts, smoking, alcohol and marijuana use,
and risky sexual activity (see the Appendix for the scor-
ing algorithm). More general behavioral problems were
ascertained using the Behavior Problem Index (BPI),
22
completed by both the youth and the primary caregiver
(the latter for comparison with earlier assessments). For
both the YRBSS and the BPI, higher scores indicate more
problems.
Finally, we asked the caregiver and the youth specific
questions about youth involvement with the justice sys-
tem. These questions included items on trouble with the
police, arrests, and time in jail. A positive event was
coded if either reported it.
Cognitive Development
Two measures of cognitive development were admin-
istered: the Weschler Abbreviated Scale of Intelligence
(WASI)
23
and the Peabody Picture Vocabulary Test-Ver-
sion III (PPVT-III).
24
The latter, a measure of receptive
vocabulary, has been used in this sample at each assess-
ment point since 3 years of age and was designated the
primary outcome because of this continuity over time.
Both tests are referenced to a mean of 100 and an SD of
15. The WASI provides 4 subscales (vocabulary, block
design, similarities, and matrix reasoning) and can gen-
erate a verbal IQ and performance IQ, as well as a full IQ
score, with only the last being considered here.
Physical Health
Physical health was characterized by youth self-report
and caregiver report on the 36-Physical Component
Summary measure.
25
This scale reflects limitations in
activities of daily living because of health, as well as
positive health. It is referenced to a mean score of 50 and
an SD of 10, with higher scores indicative of better health.
Of these measures, math and reading achievement
tests, the risk behavior scale, youth self-report on the
BPI, and the PPVT-III were considered the primary out-
comes for the analysis. However, the results for the
WASI, caregiver-reported behavior problem score, and
self-report and caregiver report on physical health are
provided for continuity with earlier reports.
Baseline Measures
As in previous analyses of the IHDP, a standard set of
prerandomization variables was used to compare partic-
ipants and nonparticipants in this assessment and to
adjust the outcomes for differences across sites and birth
weight strata. These variables included birth weight in
grams, maternal age in years, race/ethnicity (black, His-
panic and white/other), gender of child (male/female),
maternal educational attainment at the time of the birth
of the child (less than high school graduate [HSG], HSG,
and more than HSG), and Neonatal Health Index,
26
a
measure of neonatal length of stay in the hospital rela-
tive to birth weight, which serves as an indication of the
severity of the neonatal course. This index is referenced
to a mean of 100 and SD of 16. Baseline variables also
included study site: Arkansas (Little Rock, AK), Einstein
(South Bronx, NY), Harvard (Boston, MA), Miami (Mi-
ami, FL), Pennsylvania (Philadelphia, PA), Texas (Dallas,
TX), Washington (Seattle, WA), and Yale (New Haven,
CT). Gestational age at birth was also available.
Assessments at Age 8
In addition, we compared participants and nonpartic-
ipants for the cognitive, achievement, and behavioral
assessments done at 8 years of age. These measures
included the Wechsler full-scale IQ score,
27
achievement
scores in math and reading,
20
the PPVT-Revised,
28
and
behavior problem scores.
29
Analysis
Participants and nonparticipants at the 18-year assess-
ment were compared on the prerandomization variables
and 8-year outcomes noted above. A subject was con-
sidered a participant if any of the outcomes of interest
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were observed at the 18-year visit and as a nonpartici-
pant otherwise. The comparison of the differences be-
tween participants and nonparticipants in the INT and
FUO groups were evaluated by using the t statistic for
continuous measures and
2
statistics for categorical
measures.
To compare the INT and FUO groups on the outcomes
of interest at age 18, separate linear (analysis of covari-
ance) models were developed for each outcome variable
within each of 2 birth weight strata using the S-plus
software described by Venables and Ripley.
30
The same
set of 7 baseline variables measured at enrollment as
noted above was used in each model of the comparison
of the INT versus FUO. Multivariate models were used to
estimate the differences between the INT and FUO
groups to adjust for differences in sample sizes among
the sites.
14
The linear models were used for estimation of
population marginal mean values and differences (INT
versus FUO) for each outcome. The estimated marginal
means were obtained by substituting into the linear
model the average values of the covariates for a partic-
ular birth weight stratum. Nominal P values derived
from the linear models were used for primary outcome
comparisons.
We evaluated the robustness of these conventional
estimates of the difference between the INT and FUO
groups by comparing them with the results of the anal-
ysis of covariance where each of the respondents was
weighted by the inverse of the outcome-dependent es-
timated propensity score
31
to assess the effect of attrition.
We assumed that the propensity score (which, in our
analysis, is the outcome-dependent probability of ob-
serving an outcome of interest at the 18-year visit) de-
pended on the values of the full-scale IQ and child
behavior checklist at the 8-year visit and baseline char-
acteristics of a subject. Thus, for example, subjects from
Harvard with low IQs at age 8 were less likely to partic-
ipate at age 18, and the average participant with these
characteristics would be assigned higher weights (more
influence) in the propensity-adjusted analyses of the
difference between the INT and FUO groups using this
approach. Under the modeling assumptions, this method
removes nonresponse bias.
Human Subjects
The study was approved by the institutional review
boards of all participating institutions. In addition, certi-
fication of confidentiality was obtained for this phase.
Written informed consent was obtained separately for all
of the participants: study subject and caregiver.
RESULTS
Comparison of Participants and Nonparticipants at 18 Years of
Age
At age 18, 636 (64.6%) of the 985 of the participants in
the original IHDP trial were assessed: 67.4% of the INT
group and 62.8% of the FUO group (odds ratio: 1.22; P
⫽ .15; 95% confidence interval [CI]: 0.93 to 1.60). This
represents 72% of those eligible to be followed (ie, those
who had not died or refused additional participation by
8 years of age). Refusal rates were low (2.7% of the 338
in the INT group and 4.6% of the 540 in the FUO group
seen at age 8). There was 1 death (in the INT group),
which occurred after the assessment was scheduled but
before it could be completed. Because the family wished
to participate in this round and provided both caregiver
and sibling responses, this individual was considered in
the participant category. The major reason for lack of
response was the inability of the site teams to locate the
subjects, or subjects repeatedly missed appointments. As
seen in Table 1, those seen at 18 years of age did not
differ from the original sample in the baseline character-
istics except for maternal educational attainment at the
time of enrollment, race/ethnicity, and study site. In the
INT group, mothers of lower educational attainment and
Hispanic ethnicity were less likely to participate in phase
IV. These factors also influenced participation in the
HLBW INT group with the additional lower participation
among males (41.5% among participants vs 62.5%
among nonparticipants; P ⫽ .028). Within the LLBW
INT group, only race/ethnicity was a significant predic-
tor. Race/ethnicity and male gender were also associated
with participation status in the HLBW FUO group. The
effect of study site was seen in all of the groups overall
and within birth weight strata. The Einstein, Harvard,
and Washington sites had relatively lower follow-up
rates, and Arkansas, Pennsylvania, and Yale sites were
relatively higher. When participants and nonparticipants
were compared for the assessments at age 8 (Table 2),
participants in the INT group had a somewhat higher IQ,
PPVT-III, and reading and math achievement and lower
behavior problem (ie, fewer problems) scores than non-
participants. In the FUO group, participants had fewer
behavior problems than nonparticipants.
Comparison of INT and FUO Groups on Primary and Secondary
Outcomes
Because the initial trial was designed and powered to
permit comparisons within birth weight strata, and be-
cause subjects were sampled differently in each birth
weight stratum, we have displayed the results separately
for the HLBW and LLBW groups (Table 3). As in the
previous assessments at 5 and 8 years of age, no statis-
tically significant differences were seen between INT and
FUO groups in the group weighing ⱕ2000 g in compar-
isons adjusted for the baseline variables only (Table 3
line “a” for each outcome), although a difference in
reading achievement scores favoring the FUO group
achieved P ⫽ .08. When the results were also adjusted
for attrition (Table 3, line “b”), the difference in reading
favoring the FUO group was strengthened.
Although the use of the covariates was considered
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appropriate because of the differences in the original
sample sizes among sites, the effect of this adjustment
was minor. For example, the unadjusted mean PPVT-III
scores for the LLBW INT and FUO groups were 94.1 and
96.1, respectively, compared with 93.7 and 96.1 in Table
3.
In contrast, among those ⬎2000 g, there were statis-
tically significant elevations in PPVT-III and math
achievement scores favoring the INT group in the results
adjusted for the baseline covariates. The INT group ex-
perienced 5- and 6-point higher reading and math
achievement scores, respectively, with the latter at P ⫽
.01. No statistically significant difference was seen in
self-reported behavior problems or the risk behavior
scale from the YRBSS in these analyses. When the com-
parisons were adjusted for attrition, the difference in
reading achievement diminished but that for the math
achievement remained statistically significant. A differ-
ence was seen favoring the INT group on the YRBSS
score as having fewer risky behaviors (P ⫽ .05). When
the INT and FUO groups were compared on the mea-
sures of secondary outcomes, no statistically significant
differences were seen, although the difference favoring
the INT group on the full-scale IQ score among the
HLBW group (Table 4) had a P value of .07.
Fig 1 provides a summary of the published outcomes,
where comparable, from all 4 of the assessment periods.
In the HLBW group, the 14-point difference seen at age
3 diminished to ⬃4 points, but this difference has re-
mained stable and consistent over time. Likewise, the
differences in PPVT scores favoring the INT have per-
sisted after age 3. Changes in the achievement scores in
TABLE 1 Comparison of Participants and Nonparticipants in Phase IV (18 Years) According to Baseline
Characteristics and Study Arm
Characteristic INT FUO
Participant Nonparticipant Participant Nonparticipant
Total 254 123 382 226
% of total 67.4 32.6 62.8 37.2
Birth weight, g
Mean (SD) 1817 (441) 1824 (436) 1795 (465) 1758 (473)
P .89 .35
ⱕ2000 g, % 63.0 61.0 64.1 62.8
⬎2000 g, % 37.0 39.0 35.9 37.2
P .79 .81
Gestational age, wk
Mean (SD) 33.1 (2.4) 33.0 (2.8) 33.1 (2.7) 32.9 (2.9)
P .72 .37
NHI
Mean (SD) 100.6 (15.1) 100.8 (17.7) 99.4 (15.1) 100.0 (17.1)
P .93 .66
Maternal age, y
Mean (SD) 24.6 (5.8) 24.7 (6.2) 25.1 (6.2) 24.6 (6.0)
P .88 .34
Maternal education
⬍High school, % 36.6 56.1 35.9 42.0
High school, % 30.3 22.0 28.3 25.7
⬎High school, % 33.1 22.0 35.9 32.3
P ⬍.01 .32
Race/ethnicity
Black, % 50.8 58.5 53.7 49.1
Hispanic, % 7.5 14.6 9.4 14.2
White/other, % 41.7 26.8 36.9 36.7
P ⬍.01 .18
Male, % 47.2 56.9 47.1 49.1
P .10 .70
Study site (% of total)
Arkansas 14.6 8.9 17.5 5.8
Einstein 11.0 14.6 13.1 18.6
Harvard 8.7 18.7 11.5 21.7
Miami 11.8 11.4 9.9 8.0
Pennsylvania 15.4 7.3 12.0 3.1
Texas 10.2 18.7 12.3 18.1
Washington 13.0 14.6 10.2 18.1
Yale 15.4 5.7 13.4 6.6
P ⬍.01 ⬍.001
NHI indicates Neonatal Health Index.
27
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this group were generally parallel while exhibiting the
expected decline in achievement scores with aging into
the late teen years. The figure also reveals that results
from the current phase suggesting that small differences
favoring the FUO group in PPVT, IQ, and math achieve-
ment scores also emerged early and persisted.
To examine whether the results for those ⬍2000 g at
birth might reflect a heavier weighting of children with
significant neurologic complications, we reran the anal-
yses for those children who had an IQ ⬎85 at age 1 year.
Restriction of the analysis to this group led to estimate
differences in reading scores (⫺3.1 [95% CI: ⫺7.1 to
0.09], P ⫽ .13, adjusted for baseline covariates; ⫺2.8
[95% CI: ⫺6.9 to 1.2], P ⫽ .17, for the propensity-
weighted estimates) that were not statistically signifi-
cant.
We also explored differences in specific behavioral
and school outcomes. Among the INT LLBW group, 16%
had been arrested compared with 20% of the FUO group
(with P ⫽ .11, adjusted for baseline covariates and attri-
tion). The comparable figures for the HLBW group was
21% and 26%, respectively (P ⫽ .56). Approximately
12% to 13% of both birth weight groups had already
been in jail with no differences between the INT and
FUO groups. Among the LLBW group, 10% of the INT
group and 8% of the FUO group were classified as hav-
ing dropped out of school (P ⫽ .40); in the HLBW group,
it was 11% and 12%, respectively (P ⫽ .58). With regard
to ever being classified for special education, 30% of INT
group and 26% of the FUO group in the LLBW stratum
had been so classified (P ⫽ .39) and 17% and 24% of the
HLBW stratum (P ⫽ .12).
DISCUSSION
The results of this phase of the IHDP suggest a persistent
benefit of the intervention for the subset of HLBW par-
ticipants and absence or even reversal of any interven-
tion effect for the youth born weighing ⱕ2000 g. These
results parallel those seen at 8 years of age.
16
As ex-
pected, IQ and achievement scores were lower and be-
havior problem scores higher than expected population
references, reflective of patterns seen among those who
were LBW and/or premature at birth.
32
Our rates of juvenile arrest at age 18 are comparable
with those the seen in the Chicago study,
10
but the
difference between the INT and FUO groups is smaller,
4% to 5% as compared with 8% in the Chicago study,
where the difference did achieve statistical significance.
Likewise, our incarceration rates are similar to those
reported in the Abecedarian intervention group
4
but
somewhat lower than the rates in the control group. The
differences in incarceration rates also fail to achieve sta-
tistical significance. Comparisons with the Perry Pre-
school Project cannot be made, because they report the
percentage with ⱖ5 arrests at rates substantially higher
than arrest records in other studies.
Comparison of our educational outcomes with other
studies is complicated by the fact that our sample has not
yet established a post– high school educational pattern in
terms of enrollment in higher education as reported in
Abecedarian,
4
and even final high school graduation
rates are unknown. Our dropout rate is substantially
lower than the ⬃50% seen in the Chicago study,
10
as is
the difference between intervention and control groups.
Our rates of special education and differences between
INT and FUO in the HLBW group are similar to those in
the Chicago study, where the difference was highly sig-
nificant.
In this analysis, we have not examined outcomes by
prerandomization variables other than birth weight. This
decision reflects the results at age 8 where no difference
in effect size is seen at different levels of maternal edu-
cation in contrast to a hypothesized greater effect of the
intervention for children from more disadvantaged
backgrounds.
16
The persistence of an intervention effect in the HLBW
group provides substantial reinforcement to the emerg-
ing literature on longer-term effects of early educational
intervention.
4–9
First, the IHDP was implemented in 8
sites and is modeled on the Abecedarian Project,
4
argu-
ing for replicability of the results. Second, the IHDP has
been characterized as methodologically rigorous with
strict randomization and masked assessments at major
outcome points at all of the follow-up phases and has
avoided some of the concerns associated with other
projects.
8
In contrast to previous studies, which involved
largely poor, healthy children, the IHDP expands the
results of early educational intervention in 2 ways. First,
the sample is heterogeneous with regard to health, es-
pecially neurodevelopmental status, by virtue of it being
a sample of preterm, LBW children. Although not all
LBW children sustain neurologic injury,
32
being LBW
TABLE 2 Comparison of Participants and Nonparticipants in Phase
IV (18 years) According to Cognitive, Behavioral, and
Achievement Scores at Age 8
Variable INT FUO
Participant Nonparticipant Participant Nonparticipant
Full-scale IQ
Mean (SD) 87.5 (29.2) 79.1 (23.3) 86.5 (27.8) 83.4 (26.6)
P .02 .22
PPVT-III
Mean (SD) 86.1 (23.9) 80.9 (19.6) 86.2 (23.1) 83.7 (22.3)
P .07 .26
W-J reading
Mean (SD) 99.6 (20.5) 93.1 (22.2) 98.1 (21.2) 95.9 (21.1)
P .01 .30
W-J math
Mean (SD) 97.7 (23.1) 90.3 (23.3) 96.4 (21.9) 93.5 (22.1)
P .01 .16
CBCL total
Mean (SD) 30.6 (20.7) 33.7 (19.7) 30.1 (18.5) 34.1 (20.8)
P .23 .02
W-J indicates Woodcock-Johnson Achievement Test
19
; CBCL, Child Behavior Checklist.
30
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confers increased risk of neurodevelopmental disability
that may make academic achievement difficult. For ex-
ample, in unpublished analyses, children with cerebral
palsy in the IHDP experienced no advantage in cognitive
function at age 3 from the intervention. Second, the
IHDP was more heterogeneous with regard to socioeco-
nomic status than previous studies. We have docu-
mented that children of mothers with some college or
more education did not benefit from the intervention
immediately at the end of the trial.
33
Thus, although the
effects sizes are modest, they reinforce the existing litera-
ture because they reflect a more heterogeneous study pop-
ulation biased against finding a difference. It should be
noted that the pattern of persistence seen in Fig 1, includ-
ing diminishing performance on achievement testing with
age, closely parallels results for the Abecedarian Project.
18
As in the 8-year assessment, questions might be
raised about the significance of a 4-point difference in
achievement or the PPVT-III. However, it should be
noted that the difference in mean scores also indicates a
shift in the entire distribution in favor of the INT group.
In the past, we have argued that such a shift would
decrease the percentage of children classified as intellec-
tually deficient.
16
Others have also argued the impor-
tance of such differences and the potential to alter the
distribution of those who will do poorly in school.
34
The lack of persistence of an effect in the LLBW
children is also relevant to this emerging literature in
that it raises questions about greater attention to the
factors that foster or inhibit sustained effects. The LLBW
groups did initially benefit from the intervention as in-
dicated by a 6.6-point difference in IQ scores favoring
the INT group at 3 years of age.
14
Moreover, the lack of
sustained effect was not because of the experience of
very premature or very small infants, because the same
effect size is seen among those ⱕ1500 g and even ⱕ1000
g in birth weight.
35
However, differences between the
INT and FUO groups among the LLBW children disap-
pear by age 5 years.
15
One analysis suggests that the
intensity of participation may be a factor in that sus-
TABLE 3 Major Outcomes at Age 18 Years for Youth in the IHDP
Variable n Marginal
Mean Scores
Difference INT vs FUO
Estimated Value (95% CI)
P
INT FUO INT FUO
Birth weight ⬍2000 g
PPVT-III
a 154 234 93.7 96.1 ⫺2.5 (⫺5.5 to 0.5) .10
b 152 232 93.0 95.5 ⫺2.4 (⫺5.4 to 0.5) .10
Woodcock Johnson
Reading
a 153 233 92.5 96.2 ⫺3.7 (⫺7.9 to 0.4) .08
b 151 231 91.4 95.6 ⫺4.2 (⫺8.4 to 0.0) .05
Math
a 153 234 87.3 89.4 ⫺2.0 (⫺5.2 to 1.1) .21
b 151 231 86.0 88.7 ⫺2.7 (⫺5.9 to 0.6) .11
TBPI-Y
a 145 226 9.8 9.8 0 (⫺1.2 to 1.2) .98
b 144 224 9.9 10.0 0 (⫺1.2 to 1.2) .99
YRBSS
a 148 231 2.4 2.2 0.2 (⫺0.3 to 0.7) .41
b 147 229 2.4 2.1 0.3 (⫺0.2 to 0.8) .29
Birth weight ⬎2000 g
PPVT-III
a 91 132 99.6 94.5 5.1 (1.2 to 9.0) .01
b 89 132 98.8 95.0 3.8 (⫺0.3 to 7.8) .07
Woodcock Johnson
Reading
a 90 130 100.4 95.0 5.3 (⫺0.4 to 11.1) .07
b 88 130 98.9 95.7 3.3 (⫺2.5 to 9.1) .27
Math
a 91 130 95.5 89.4 6.1 (1.6 to 10.6) .01
b 89 130 94.9 89.8 5.1 (0.6 to 9.7) .03
TBPI-Y
a 85 126 10.2 9.3 0.9 (⫺0.6 to 2.3) .23
b 83 126 10.4 9.3 1.1 (⫺0.4 to 2.6) .15
YRBSS
a 89 127 2.4 2.9 ⫺0.5 (⫺1.3 to 0.3) .19
b 87 127 2.2 3.0 ⫺0.7 (⫺1.5 to 0.0) .05
TBPI-Y indicates Total Behavior Problem Index-Youth Self-Report; a, adjusted for all the variables in Table 1 except gestational age; b, adjusted for
variables in Table 1 except for gestational age and attrition.
PEDIATRICS Volume 117, Number 3, March 2006 777
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tained effects at age 8 were seen among those attending
⬎400 days of center-based education (out of a maximum
of 500) during the intervention period.
36
In addition, we
speculate that earlier entry into special education may also
play a role and needs additional investigation.
Several limitations affect the interpretation of our
study. The first is the lower response rate than previous
rounds of assessment in the IHDP, particularly with loss
among more disadvantaged children and those study
participants with lower previous cognitive development.
Our adjustment of the results for these factors suggests
that the losses to the cohort do not significantly affect
the results, but differences may have occurred in un-
measured factors.
Second, the age of assessment, 18 years, may not be
optimal in identifying economically important out-
comes, such as higher educational attainment, definitive
occupational status, and eventual income. In the Perry
Preschool Project, economically significant differences
are seen at 27 and now 40 years of age.
6,8
Even at 21
years of age, the Abecedarian Project
4
did not detect
significant differences in employment but, in results par-
allel to ours, did find differences in risk behaviors. They
did, however, find an intervention advantage in the
proportion enrolled in a 4-year college or university.
Third, because our study sample is not all disadvan-
taged, the power to detect significant differences in some
areas is limited. As noted earlier, arrest rates in the Perry
Preschool Project
8
are substantially higher than other
longer-term follow-up studies of early education. With
all rates of adverse outcomes, such as arrest or special
education classification, differences favoring the INT
group, especially the HLBW youth, are either similar or
about half the effect size. Thus, we would have needed a
substantially larger sample, in the order of the 1500 in
the Chicago study,
10
to achieve statistical significance.
This finding also suggests caution in extrapolating cost-
effectiveness arguments of early educational interven-
tion based on reductions in costs among populations
with less risk of poor educational attainment and crim-
inal behavior.
Despite these limitations, this phase of the IHDP pro-
vides important support for the efficacy of early educa-
tional interventions in the longer-term outcomes of chil-
dren. It also presents significant challenges in identifying
those who would most benefit and those who may need
continuing support to achieve academically. However,
the results provide support for extending such educa-
tional opportunities to a broader spectrum of children
than included in previous studies.
TABLE 4 Secondary Outcomes at Age 18 Years of Youth in the IHDP
Variable n Marginal
Mean Scores
Difference INT vs FUO
Estimated Value (95% CI)
P
INT FUO INT FUO
Birth weight ⬍2000 g
WASI full-scale IQ
a 154 236 89.4 91.2 ⫺1.8 (⫺4.5 to 0.9) .19
b 152 233 88.5 90.7 ⫺2.2 (⫺5.0 to 0.6) .12
TBPI-CAR
a 144 234 9.2 9.1 0.2 (⫺1.2 to 1.6) .81
b 142 230 9.9 9.3 0.5 (⫺0.9 to 2.0) .46
PCS-CAR
a 155 238 53.6 54.0 ⫺0.4 (⫺1.6 to 0.8) .51
b 153 235 53.3 54.0 ⫺0.6 (⫺1.9 to 0.6) .31
PCS-YA
a 149 234 53.4 54.2 ⫺0.8 (⫺2.3 to 0.7) .31
b 148 232 53.4 54.1 ⫺0.8 (⫺2.3 to 0.8) .33
Birth weight ⬎2000 g
WASI full-scale IQ
a 92 132 94.6 91.3 3.3 (⫺0.3 to 6.9) .07
b 90 132 93.7 92.0 1.7 (⫺2.0 to 5.3) .38
TBPI-CAR
a 82 124 8.5 9.3 ⫺0.9 (⫺2.7 to 0.9) .34
b 80 123 8.9 9.6 ⫺0.7 (⫺2.6 to 1.1) .45
PCS-CAR
a 86 131 55.5 54.9 0.6 (⫺1.0 to 2.1) .47
b 84 130 55.5 55.0 0.6 (⫺1.0 to 2.1) .48
PCS-YA
a 90 129 55.1 54.3 0.9 (⫺0.9 to 2.7) .34
b 88 129 55.3 54.6 0.7 (⫺1.1 to 2.5) .46
TBPI-CAR indicates Total Behavior Problem Index by caretaker report; PCS-CAR, Physical Health Scale by caretaker report; PCS-YA, Physical Health
Scale by youth report; a, adjusted for all the variables in Table 1 except gestational age; b, adjusted for variables in Table 1 except for gestational
age and attrition.
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APPENDIX
The YRBSS questionnaire has no established scoring al-
gorithm. We identified questions in 6 risk areas (antiso-
cial behavior, suicidal ideation/attempt, smoking, alcohol
usage, and marijuana usage) considered most relevant to
the study. Because there were different numbers of
items in each of these categories, a simple sum across the
questions would have weighted some areas more than
others. Thus, to obtain an interval score for risk behav-
iors, we developed a 3-level score for each area, assign-
ing the numeric values of 0, 1, and 2 to the low, me-
dium, and high scores. Cut points were assigned so that
⬃15% of the group fell into the highest-risk group, the
majority (⬎60%) in the low-risk group, and the remain-
der in the moderate-risk group. We summed these area-
dependent scores to produce an overall score of risky
behavior. This approach parallels that of Flisher et al,
37
in
a report of behavior in a community sample of children
and adolescents.
1
Of the 636 subjects, data for this anal-
ysis was missing on 5%. The resulting score had a mean
of 2.4 in our study population, with an SD of 2.6 and a
range of 0 –11. Initial bivariate comparisons of INT and
FUO groups were done, therefore, using nonparametric
techniques. Adjusting for baseline covariates and attri-
tion, however, relied on parametric statistics as described
in “Methods.”
ACKNOWLEDGMENTS
This study was supported through grant 039543 from
the Robert Wood Johnson Foundation. The funder pro-
vided funding for the data collection and reviewed both
the proposal and the final results.
FIGURE 1
Cognitive and achievement scores at different assess-
ment points in the IHDP for the heavier birth weight
group. A, IHDP: IQ results over time—HLBW group
(adjusted for baseline covariates;
a
P ⬍ .05). B, IHDP:
PPVT results over time—LLBW group (adjusted for
baseline covariates;
a
P ⬍ .05). C, IHDP: Woodcock-
Johnson Achievement Test reading results over
time—HLBW group (at 18, P ⫽ .10; adjusted for base-
line covariates, P ⫽ .05). D, IHDP: Woodcock-Johnson
Achievement Test math results over time—HLBW
group (adjusted for baseline covariates;
a
P ⬍ .05). E,
IDHP: PPVT results over time—LLBW group (adjusted
for baseline covariates;
a
P ⬍ .05). F, IDHP: IQ results
over time—LLBW group (adjustedfor baseline covari-
ates;
a
P ⬍ .05). G, IDHP: Woodcock-Johnson Achieve-
ment Test reading results over time—LLBW group (at
18, P ⫽ .10; adjusted for baseline covariates). H, IDHP:
Woodcock-Johnson Achievement Test math results
over time—LLBW group (adjusted for baseline covari-
ates). Baseline covariates: birth weight, maternal age
at youth’s birth, race/ethnicity, child gender, maternal
educational attainment at youth’s birth, Neonatal
Health Index,
26
and study site. Values for 3- and 5-year
assessments are from ref 16; values for 8-year assess-
ments are from ref 16.
PEDIATRICS Volume 117, Number 3, March 2006 779
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For previous participants in the IHDP, see refs 14 –16.
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DOI: 10.1542/peds.2005-1316
2006;117;771Pediatrics
and Patrick H. Casey
C. Bernbaum, Charles R. Bauer, Camilia Martin, Elizabeth R. Woods, Anne Martin
JudyJennifer Yu, Mikhail Salganik, David T. Scott, Forrest C. Bennett, Libby L. Kay,
Marie C. McCormick, Jeanne Brooks-Gunn, Stephen L. Buka, Julie Goldman,
of Age for the Infant Health and Development Program
Early Intervention in Low Birth Weight Premature Infants: Results at 18 Years
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