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Computerized crime linkage systems are meant to assist the police in determining whether crimes have been committed by the same offender. In this article, the authors assess these systems critically and identify four assumptions that affect the effectiveness of these systems. These assumptions are that (a) data in the systems can be coded reliably, (b) data in the systems are accurate, (c) violent serial offenders exhibit consistent but distinctive patterns of behavior, and (d) analysts have the ability to use the data in the systems to link crimes accurately. The authors argue that there is no compelling empirical support for any of the four assumptions, and they outline a research agenda for testing each assumption. Until evidence supporting these assumptions becomes available, the value of linkage systems will remain open to debate.
Criminal Justice and
The online version of this article can be found at:
DOI: 10.1177/0093854811435210
2012 39: 620Criminal Justice and Behavior
Craig Bennell, Brent Snook, Sarah Macdonald, John C. House and Paul J. Taylor
Computerized Crime Linkage Systems : A Critical Review and Research Agenda
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International Association for Correctional and Forensic Psychology
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© 2007 American Association for Correctional and Forensic Psychology
CRIMINAL JUSTICE AND BEHAVIOR, Vol. 39 No. 5, May 2012 620-634
DOI: 10.1177/0093854811435210
© 2012 International Association for Correctional and Forensic Psychology
AUTHORS’ NOTE: Correspondence concerning this article should be addressed to Craig Bennell,
Department of Psychology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada;
e-mail :
A Critical Review and Research Agenda
Carleton University
Memorial University of Newfoundland
Royal Newfoundland Constabulary
Lancaster University
Computerized crime linkage systems are meant to assist the police in determining whether crimes have been committed by
the same offender. In this article, the authors assess these systems critically and identify four assumptions that affect the
effectiveness of these systems. These assumptions are that (a) data in the systems can be coded reliably, (b) data in the sys-
tems are accurate, (c) violent serial offenders exhibit consistent but distinctive patterns of behavior, and (d) analysts have the
ability to use the data in the systems to link crimes accurately. The authors argue that there is no compelling empirical support
for any of the four assumptions, and they outline a research agenda for testing each assumption. Until evidence supporting
these assumptions becomes available, the value of linkage systems will remain open to debate.
Keywords: crime linkage systems; comparative case analysis; behavioral linking; serial crimes; behavioral consistency;
n important task in some police investigations is to determine whether or not a set of
crimes has been committed by the same offender (Grubin, Kelly, & Brunsdon, 2001).
To assist with this linking task, law enforcement agencies have developed computerized
crime linkage systems that contain offense, offender, and victim information, all of which
are extracted from investigative files (Collins, Johnson, Choy, Davidson, & MacKay,
1998). The analysis of data contained within these systems is assumed to increase the prob-
ability of identifying a crime series. However, despite the widespread use of some linkage
systems, the assumptions underlying these systems have seldom been tested empirically.
The goal of this article is to examine these assumptions in light of available evidence and
to propose an agenda for future research that can further refine our understanding of when
such systems can be effective. However, before turning to our primary task, we outline the
origins of crime linkage systems and describe some of their possible functions.
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Crime linkage systems can be traced back to the development of the Federal Bureau of
Investigation’s (FBI) Violent Criminal Apprehension Program (ViCAP) in 1985. ViCAP
was developed for the laudable purpose of avoiding “linkage blindness,” a term used to
describe the absence of communication between law enforcement agencies that might be
investigating related cases (Egger, 1984). The ViCAP initiative sought to reduce this prob-
lem by helping agencies determine whether or not linked crimes were being committed
across jurisdictional boundaries (FBI, n.d.). To accomplish this goal, information about
violent offenses was entered into a computer database and analyzed to identify crimes that
showed distinct patterns of similarity that might reflect linkages. To this day, ViCAP
remains a nationwide data information system for collecting, sorting, and analyzing solved
and unsolved cases of violent crime (FBI, n.d.).
Other systems were developed subsequently to assist with linkage analysis. These
include Washington State’s Homicide Investigation Tracking System, New Jersey’s
Homicide Evaluation and Assessment Tracking System, Iowa’s Sex Crimes Analysis
System, the Royal Canadian Mounted Police’s Major Crime File, and its successor, the
Violent Crime Linkage Analysis System (ViCLAS; see Collins et al., 1998, for a list of
additional systems). Although we believe that most of the issues discussed in this article
apply to all linkage systems, our arguments often focus on ViCLAS because it is the most
frequently used of all linkage systems and is generally considered the “gold standard”
(Collins et al., 1998, p. 277). Currently, there are ViCLAS centers in every Canadian prov-
ince, with the exception of Prince Edward Island, and its use is mandated in two provinces
(Ontario and Quebec). ViCLAS is also reportedly used as part of a repertoire of investiga-
tive tools in the following locations: Australia, Austria, Belgium, Czech Republic, France,
Germany, Ireland, the Netherlands, New Zealand, Switzerland, the United Kingdom, and
two U.S. states (Indiana and Tennessee; Royal Canadian Mounted Police [RCMP], n.d.).
Linkage systems differ from each other in a variety of important ways, and the same
system may even be used differently across jurisdictions (e.g., Witzig, 2003). However,
there is arguably a core procedure that is generally applicable to most systems when link-
ing several crimes. As an example, in ViCLAS, the general linking procedure consists of
five broad steps (RCMP, n.d.). First, data related to specific crime types are collected and
recorded, usually with the assistance of a coding manual.
Second, the data are scrutinized
for the purpose of quality assurance, and attempts are made to fix any errors that were made
during the data coding phase. Third, data are entered into a computer database that contains
equivalent information about other crimes. Fourth, the data are examined for potential
crime linkages, typically by someone who is trained to search the database. Fifth, once the
search for linked crimes is complete, relevant investigators are informed about potential
linkages. These investigators are encouraged to confirm or eliminate the potential linkages
through further investigation.
There are a number of different functions that can potentially be served by crime linkage
systems. The first and most obvious use is to conduct linkage analysis by searching the
database to identify crimes that share similar, but distinctive, features. Single aspects of a
crime can be used to conduct these searches, or the user can generate search queries that
include complex combinations of the coded variables. One aspect of the data that is some-
times relied on for this purpose is the offender’s behavior at the crime scene (Martineau &
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Corey, 2008), although searches can be based on offense, offender, and/or victim informa-
tion. Searches using crime scene behaviors can rely on aspects of an offenders modus
operandi (MO), which is defined as a behavior or set of behaviors exhibited by the offender
that allow him or her to successfully carry out the crime (Kangas, 2001; Martineau &
Corey, 2008; Ressler, Burgess, & Douglas, 1988). However, because MO can change
across an offender’s crimes (Douglas & Munn, 1992), some analysts may also search for
“behavioral signatures” (Gault, 2010; Keppel, 2000; Keppel, Weis, Brown, & Welch,
2005). Unlike MO, behavioral signatures are thought to be unnecessary for the successful
completion of a crime but instead represent distinctive behaviors exhibited by an offender
across his or her crimes to satisfy some psychological need (e.g., positioning a victim’s
body in a particularly degrading manner after death; Douglas & Munn, 1992).
Second, a number of individuals have suggested that crime linkage systems can serve
other investigative functions that go beyond the specific task of linking crimes. For exam-
ple, one function is appraisal, in that completing a coding booklet can provide the means
to evaluate the effectiveness of an investigation. As Cooper (2007) argues with respect to
ViCAP, “[T]he ViCAP form . . . serves as an excellent reference guide while conducting a
thorough and well thought-out investigation. . . . If the questions posed by the ViCAP form
are completed, it can be presumed that the investigation is complete and thorough.”
Given how comprehensive most coding booklets are, this argument likely applies to other
linkage systems as well.
Third, although limited in practice, crime linkage systems could also potentially be used
in court, where questions are sometimes raised about whether or not a defendant is respon-
sible for a series of crimes (Bosco, Zappalà, & Santtila, 2010; Meyer, 2007; Ormerod &
Sturman, 2005). Law enforcement personnel have provided testimony in court about the
likelihood of multiple crimes being committed by the same offender on the basis of distinc-
tive crime scene behaviors (e.g., Labuschagne, 2006; State v. Code, 1994; State v. Pennell,
1989; State v. Prince, 1992). However, when presenting their testimony, these individuals
have typically not relied on linkage systems to generate their testimony. Several recent
court cases have stressed the importance of basing such testimony on reliable databases
(e.g., State v. Fortin, 2004). One advantage of having access to a large database of crimes
is that it will allow the courts to determine, in a more precise fashion, the degree to which
a crime scene behavior (or set of behaviors) is truly distinctive.
Finally, carefully recorded crime data stored in a well-designed crime linkage system can
also provide the basis for important research studies, only some of which will relate to link-
age analysis. For example, data extracted from linkage systems have already been used to
conduct interesting studies of serial homicide behavior (e.g., Fritzon & Garbutt, 2001), rape
typologies (e.g., McCabe & Wauchope, 2005), criminal profiling (e.g., Kocsis, Cooksey, &
Irwin, 2002), and child care providers who commit sexual offenses (e.g., Moulden,
Firestone, & Wexler, 2007).
Despite the fact that differences can exist in the way crime linkage systems are utilized,
even when the same system is used in different jurisdictions, we suggest that these systems
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are based on a number of assumptions that override these differences. There are at least
four assumptions that are important to consider, given that they will affect the effectiveness
of these systems. These assumptions are that (a) data contained in the systems can be coded
reliably, (b) data contained in the systems are sufficiently accurate to draw meaningful
inferences, (c) violent serial offenders exhibit consistent but distinctive patterns of behavior
across their crimes that will enable the linking process, and (d) analysts possess the ability
to identify such patterns and link crimes accordingly. In the sections that follow we discuss
each of these assumptions and propose future research to examine them. The research
agenda we propose can contribute to the effectiveness of linkage systems, both as a research
tool and as a tool for use in police investigations.
Evidence for the reliability of data coding. Perhaps the most fundamental assumption
underlying the use of crime linkage systems is that the data contained in the systems are
reliable. The primary type of reliability of concern here is interrater reliability. A test of
interrater reliability in this context would involve determining how often two or more cod-
ers (e.g., different investigators) enter the same information into the coding booklet, or
system, when applying the same coding categories to the same case. For example, it is
assumed that two investigators exposed to the same case material would each record the
same occupation for the victim of the crime. In scientific research, a minimum level of 80%
agreement is typically required to trust the data on which inferences and conclusions are
drawn (e.g., Hartmann, 1977). Arguably, a similarly high level of interrater agreement
should be demanded in the law enforcement context, where the inferences being drawn are
Knowing how reliable data are in this context is critical because the validity of infer-
ences drawn from the data contained in linkage systems depends on a high degree of inter-
rater reliability. Despite the importance of reliability, we are aware of only two studies that
have examined this issue. In one study, Martineau and Corey (2008) provided 237 police
officers with either a sexual assault or homicide vignette (a two-page summary of the case)
and asked them to complete a ViCLAS booklet. The officers were also given the ViCLAS
Field Investigators Guide—a resource that contains explanations of each question found
in a ViCLAS booklet—to assist them with their task. Once completed, Martineau and
Corey calculated three interrater reliability measures.
In terms of overall percentage agreement, Martineau and Corey (2008) reported a rate
of 88% agreement for the sexual assault case and 79% agreement for the homicide case—
both of which appear acceptable. However, these reliability values are inflated because of
the large contribution of nonoccurrence agreement between the investigators (i.e., instances
where investigators agreed that something did not occur). This is problematic for two
related reasons. First, although it is useful for investigators to agree on what did not occur
in a case (e.g., that the weapon was not a knife, or a bat, or a hammer, or a rock, etc.), it is
arguably more important that investigators agree on what did occur (e.g., that the weapon
was in fact a gun). Thus, the factors contributing to the high level of overall agreement in
Martineau and Corey’s study are not “equal” in value. Second, the level of overall agree-
ment that is found for a specific variable is dependent on the number of coding options
available for that variable. For example, if there are 10 options available for a particular
variable under study, such as the type of weapon used, then under a scenario in which only
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one option is correct (i.e., the single weapon that was used), two investigators are inevitably
going to achieve a high level of overall agreement. The only two outcomes for the afore-
mentioned example are that officers will agree 8 out of 10 times (80%) or 10 out of 10
times (100%).
In coding situations where there are many opportunities to agree on what did not happen,
a more sensitive and appropriate measure of interrater reliability is occurrence agreement
(vs. nonoccurrence agreement, or overall agreement; see Hartmann, 1977, for an in-depth
discussion of these issues). Occurrence agreement is defined as the number of instances
where two raters indicate that a particular piece of information was present in a vignette (or
case file), divided by the total number of instances where at least one of the two observers
indicated that a piece of information was present, multiplied by 100. When Martineau and
Corey (2008) calculated occurrence agreement values, the results were a less impressive
38% agreement for the homicide case and 25% agreement for the sexual assault case.
Although certain variable categories were coded in a somewhat reliable fashion (>50%
agreement), the majority of categories were not. For the homicide vignette, they found an
occurrence agreement of 4% for information about the crime scene, 9% for information
about the offense, 13% for information about the offender, 23% for information pertaining
to administration questions, 27% for information about the deceased victim, and 32% for
information about the victim. Similarly, for the sexual assault vignette, they found an
occurrence agreement of 5% for information about the biological sample, 10% for the
scene information, 13% for offense information, 13% for offender information, 18% for
victim information, and 25% for information pertaining to administration questions. These
low percentages demonstrate that officers disagreed with each other about what was pre-
sent in the vignettes more than they agreed.
In a second more recent study, Snook, Luther, House, Bennell, and Taylor (2012) tested
10 police officers to assess the interrater reliability associated with ViCLAS variables. The
sample was a relatively homogeneous group of officers from a Canadian police organiza-
tion. All of the officers investigate ViCLAS-appropriate crimes as part of their job and are
in a position to complete ViCLAS booklets. Unlike the study by Martineau and Corey
(2008), the officers in this study were provided with a complete case file to code rather than
a short vignette. The case file was longer and more detailed than the material used by
Martineau and Corey and is more similar to the material that would be coded in naturalistic
For reasons outlined above, Snook et al. (2012) focused on occurrence agreement within
their study, and consistent with the results reported by Martineau and Corey (2008), the
results indicated low levels of reliability. More specifically, of the 106 variables that were
examined in this study, the average level of occurrence agreement was 30.77%. Only 11
(10.38%) of the variables that were coded reached an acceptable level of agreement (i.e.,
80%). When the 106 variables were categorized into eight sections, the levels of occurrence
agreement ranged from as high as 63% for information pertaining to administrative ques-
tions to as low as 2% for information related to weapons. Every category other than the one
containing administrative questions was less than 50%, which raises serious questions
about whether ViCLAS data can be coded reliably.
If the aforementioned values are representative of the reliability of ViCLAS data, it
would be imprudent to draw inferences from that data. It is difficult, however, to determine
conclusively whether or not these findings reflect the reliability of ViCLAS data because
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both studies are somewhat artificial. Indeed, the values reported above may be an underes-
timation of the true levels of reliability because there was no pressure on the participants
to perform in a conscientious manner. Such pressures may be present in naturalistic settings
and could increase the effort made by coders and, as a consequence, the reliability of the
data. However, equally, the reported values in these two studies may be an overestimation
of the true values. If investigators cannot achieve reliability when reviewing material under
ideal laboratory-type coding conditions, it could be argued that interrater agreement would
worsen under naturalistic conditions where, for example, distractions are more common.
What is not debatable is the fact that little is currently known about the reliability of the
data contained in crime linkage systems such as ViCLAS.
Future research on issues of data reliability. In terms of a research agenda for the future,
it is imperative that studies of interrater reliability be conducted for all linkage systems. The
studies by Martineau and Corey (2008) and Snook et al. (2012) provide models for
conducting such studies. We encourage researchers to place greater emphasis on certain
forms of reliability over others when conducting such studies (e.g., occurrence agreement
vs. nonoccurrence agreement) and to explore other potential reliability statistics, such as
Krippendorffs alpha (Krippendorff, 2004). We also encourage researchers to use research
stimuli that match as closely as possible the type of material that would be coded in real-
world settings, as Snook et al. did in their recent study, because the amount of investigative
material that needs to be processed, and its complexity, could have an impact on the degree
of interrater reliability that is achieved. One likely outcome of this type of research will be
an enhanced knowledge of the sections contained in coding booklets that might be prob-
lematic with respect to interrater reliability. This information could then be used to modify
relevant parts of the coding framework or to provide enhanced training on sections identi-
fied to be troublesome. Ideally, the impact of these changes would also be evaluated to
determine the extent to which they positively affect the degree of interrater reliability that
is achieved.
It will also be important to evaluate attempts that are being made by police organizations
to increase the reliability of linking data. The RCMP, for example, has created the Field
Investigators Guide for ViCLAS, which attempts to provide investigators with clear defi-
nitions of the variables in the ViCLAS coding book, and they have also implemented elec-
tronic ViCLAS coding booklets, which may increase the level of interrater reliability
associated with ViCLAS data by making the coding task easier and less time-consuming
(thereby decreasing coding errors; RCMP, n.d.). Other police organizations have central-
ized the data coding process (Abraham & O’Dwyer, 2011), which presumably increases the
likelihood that the coders have the time, commitment, and expertise to enter the data care-
fully and correctly. Although these types of changes to the linking process are potentially
useful, evaluative research assessing the impact of these innovations on data reliability will
be an important undertaking.
Evidence for the accuracy of data coding. Another assumption underlying crime linkage
systems, at least when applied to certain tasks, is that data entered into the systems accu-
rately reflect what occurred in the criminal event (Martineau & Corey, 2008). In scientific
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terms, this is an assumption about the validity of the data: that they represent what they are
supposed to represent. This assumption is important because the “quality of the information
generated from a database is only as good as the accuracy of the data contained in the
database” (Morley & Parker, 2009, p. 599). Although it is technically possible to use reliably
coded but invalid data to establish crime linkages, such a system would be operating
atheoretically, without any rationale for why the crimes are able to be linked. Without this
rationale, it would not be possible to identify the general conditions under which the system
will or will not work.
As far as we are aware, there has been no evaluation of the extent to which data stored in
linkage systems are valid. Each question included in a coding booklet provides an opportu-
nity for errors to creep into the system, and one ought to be concerned in this setting that the
nature of the data coding and entry exercises can potentially result in an increase in errors.
For example, the lengthy, repetitive nature of the coding task could result in an unreasonably
high number of coding errors (Healy, Kole, Buck-Gengler, & Bourne, 2004), where items
that should be coded as being present (or absent) in a crime are incorrectly coded as being
absent (or present). This would naturally influence the reliability of the coded data, but it
will also negatively affect the accuracy of the data (e.g., making it appear that crimes were
committed in a way that they were not). There are factors present in naturalistic police set-
tings that may counteract these problems, such as the level of conscientiousness that may be
shown by individuals when coding real cases, but whether or not these factors positively
affect the accuracy of linking data is an empirical question that requires testing.
Future research on issues of data accuracy. As is the case with interrater reliability,
examinations of data accuracy are urgently required for all linkage systems. Ideally, these
examinations will take place in naturalistic settings, using genuine crimes and data coders
who are operating under real-world conditions. A useful alternative to field tests, however,
is laboratory studies that allow researchers to gauge the degree of data accuracy associated
with a particular linkage system. For example, as done routinely in medical settings (e.g.,
Samuels, Appel, Reddy, & Tilson, 2002), the accuracy of data coding could be tested easily
using the details of solved cases. The results of these tests could be used to gauge the extent
to which police organizations should trust the data being entered into linkage systems. Such
research could also facilitate attempts to maximize data accuracy. For instance, if studies
could identify aspects of the data entry process (e.g., variable definitions included in a cod-
ing guide) that are related to coding and entry errors, this information could then be used
to make improvements. Likewise, such studies could provide quantitative estimates of
accuracy for use when evaluating modifications to a linkage system, which are often
designed to increase data accuracy.
Most police organizations appear to be aware of issues that may negatively affect data
accuracy, and some have even taken steps to minimize their impact. For example, recogniz-
ing that some level of human error is inevitable when coding files, numerous organizations
have put quality assurance mechanisms in place in an attempt to identify coding errors and
correct them before the data are entered into the linkage system (e.g., RCMP, n.d.). We are
encouraged by these attempts and think they hold promise. However, evaluative studies are
needed to ensure that the mechanisms being put into place are effective. Quality assurance
checks will also work only to the extent that they are being utilized reliably and as intended,
so the degree to which these checks are being complied with needs to be confirmed.
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Evidence for consistency and distinctiveness. Albeit implicit, the third assumption made
by some developers and users of crime linkage systems is that violent serial offenders will
exhibit behaviors across their crimes that are relatively stable and distinctive when com-
pared to behaviors exhibited by other offenders. This assumption is important because, as
indicated above, MO behaviors and/or behavioral signatures often seem to be relied on for
linking crimes (e.g., Gault, 2010; Kangas, 2001; Keppel, 2000; Keppel et al., 2005; Mar-
tineau & Corey, 2008; Ressler et al., 1988). For example, as Martineau and Corey (2008)
state in their study of ViCLAS, “[W]hen an analyst identifies a number of cases that share
significant behavioral similarities . . . the analyst will link the cases to form a potential
series” (p. 52).
The assumption that offenders will exhibit a distinctive MO across their crimes appears
to originate from the view that behavior is determined primarily by internal traits, or dis-
positions to behave in a particular way (Cervone & Shoda, 1999). If personal traits are the
primary determinant of behavior, it would be reasonable to expect people to exhibit distinc-
tive patterns of behavior in a stable fashion across situations. However, research has dem-
onstrated that situational factors also play a key role in determining how people behave,
which explains the low levels of behavioral consistency that are often found (Mischel,
1968). When stable patterns of behavioral distinctiveness are found in the noncriminal
domain, they are most often found across situations that are viewed as psychologically
similar by the individual being observed (e.g., Shoda, Mischel, & Wright, 1994), or for
behaviors that are largely under the control of the individual, rather than a product of the
situation (e.g., Funder & Colvin, 1991).
Although only limited research exists for the types of violent crimes included in most
crime linkage systems, a criminal’s MO, much like his or her noncriminal behavior,
appears to be determined by both personal preferences to behave in a particular way and a
range of situational factors (Woodhams, Hollin, & Bull, 2008).
For example, although a
serial rapist may have a preferred behavioral style when committing his or her crimes (e.g.,
a disposition favoring pseudo-intimate interactions; Canter, Bennell, Alison, & Reddy,
2003), the behavior of the offender may change (e.g., become more hostile) if he or she
experiences a high level of victim resistance in a particular crime. It should come as no
surprise then that although very high levels of consistency are sometimes reported in the
literature (e.g., Melnyk, Bennell, Gauthier, & Gauthier, 2011), the majority of research
examining the MOs of violent offenders has found low to moderate levels of behavioral
consistency (e.g., Bateman & Salfati, 2007; Bennell, Jones, & Melnyk, 2009; Grubin et al.,
2001; Santtila et al., 2008; Santtila, Junkkila, & Sandnabba, 2005; Sjöstedt, Långström,
Sturidsson, & Grann, 2008). For example, Sjöstedt et al. (2008) used kappa statistics to
assess the temporal stability of MOs exhibited by 75 Swedish sex offenders who recidi-
vated. When comparing each offenders prior sex offense to his first reoffense, low kappa
scores were found for the majority of MO features that were examined (e.g., ranging from
κ = .22 to κ = .34 for variables such as noncontact offense, physical contact, penetration,
death threat, and victim injury). The only MO feature that was relatively stable was victim
choice, although stability varied substantially as a function of victim type (ranging from κ
= .79 for male victim to κ = .49 for stranger victim). Given these sorts of results, linkage
analysts must be extremely cautious when relying on MO indicators to link violent crimes
until research emerges that can inform their selection of useful linking behaviors.
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The assumption that signature behaviors may be useful for linkage analysis seems to be
based on the belief that signatures instantiate offenders’ “scripts” that are typically well
rehearsed, deeply engrained, and rooted in personal fantasies (Canter & Heritage, 1990;
Davies, 1992; Hazelwood & Warren, 1990). In contrast to MO, we are not aware of any
empirical, published research that has examined the potential value of behavioral signa-
tures for linking crimes (at least not using commonly accepted definitions of behavioral
signatures; see Bateman & Salfati, 2007). Although case studies have been presented to
support the idea that signature behaviors can be identified and used to link serious violent
crimes (e.g., Douglas & Munn, 1992; Keppel, 1995, 2000; Keppel & Birnes, 1997; Keppel
et al., 2005), such anecdotes may not be generalizable.
Of course it might be possible to link crimes without relying on MO or behavioral signa-
tures. Indeed, other data that are stored in linkage systems, such as offender descriptions or
victim information, could potentially be used for this purpose. However, to the extent that
behavioral information is relied on, caution is warranted when considering the links that are
established. The potential dangers of using behavioral information for linking purposes
should be made clear to the individuals who carry out linkage analysis and to the investiga-
tors provided with the results of such analysis. Based on our knowledge of Canadian training
programs (e.g., for ViCLAS analysts), this message is being delivered to the people involved
in conducting the analysis. However, it is unclear whether this message is influencing the
way in which analysts operate and the subsequent advice being passed on to investigators.
Future research on issues of consistency and distinctiveness. As we have just argued, the
task of linking crimes to a common offender sometimes depends on there being evidence
that offenders display a relatively high level of behavioral consistency and distinctiveness
across the crimes they commit. Although some research has examined this issue in relation
to MO, we are aware of no empirical research examining behavioral signatures, as tradi-
tionally defined. Indeed, we still do not know whether linkage analysts can identify behav-
ioral signatures across various types of crimes, if they are in fact exhibited, or the extent to
which these signatures are useful for establishing crime linkages. Research in this area
should build on existing research (see Woodhams, Hollin, & Bull, 2007, for a review) by
striving to identify the conditions under which consistency and distinctiveness will be
found (for both MO and signatures). This research should be conducted using a range of
crime types, especially those crimes that are entered into crime linkage systems (e.g., vio-
lent interpersonal crimes). Clearly, more research also has to be conducted to determine
how the analysis of crime scene behaviors (the primary focus in most linking research) can
be integrated into the analysis of other potential linking factors, such as physical evidence,
offender characteristics, or victim descriptions.
Research of the type described in the previous paragraph could inform the construction
of more streamlined coding books, which might persuade more investigators to complete
them (a common problem with many linkage systems; RCMP, n.d.). This research will also
inform linkage analysts about what behaviors to focus on when linking crimes, and in what
order. Finally, this research could result in algorithms that accomplish much of the linking
work for the analyst, in a similar way to what is happening in the risk assessment field (e.g.,
Quinsey, Harris, Rice, & Cormier, 2006). It is interesting that attempting to derive such
algorithms provides a complementary test of the capacity of analysts to link crimes, since
the absence of any successful algorithm suggests that no linear combination of evidence
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could be used for this purpose. This finding would demand that some penetrating questions
be asked of how exactly analysts are undertaking and achieving the linking task success-
fully, assuming that they are.
Evidence for linking ability. The last assumption is that people who have received spe-
cialized training to link crimes possess the ability to identify serial crimes contained in
linkage systems. We are not aware of any research that has examined the degree to which
trained linkage analysts can make linking decisions accurately. Nor do we know of any
research that has examined performance in the types of linking tasks that analysts actually
face in naturalistic settings (e.g., the factors on which linking decisions are based in exist-
ing studies are almost always restricted to crime scene behaviors, which represent only a
subset of the variables available to analysts in the real world, and the samples of crimes that
are presented to participants in these studies often bear little resemblance to the complex
samples of linked, unlinked, and one-off crimes that linkage analysts have to contend with).
The only research available that provides a sense for how effective people are at identifying
linked crimes has been conducted using law enforcement personnel (and members of the
public) who have not received formal training in linkage analysis. As indicated above, this
research also tends to use linking tasks that are relatively low in ecological validity.
The first of these studies was conducted by Canter and his colleagues (1991). Canter
et al. provided 32 detectives in the United Kingdom the crime scene descriptions of
12 sexual attacks committed by four known offenders (three crimes per offender). Their
task was to read the descriptions, identify features of the crimes that are useful for linking
purposes, and decide which of the crimes were linked. Out of a possible 12 correct links,
the modal result (10 detectives) was 3 correct links. One detective identified no correct
links, and the highest number of correct links, which were identified by three detectives,
was 8. The results for all the other detectives in the study fell between these two extremes.
A similar study by Santtila, Korpela, and Häkkänen (2004) examined the ability of four
distinct groups of individuals to link vehicle offenses accurately. They presented experienced
vehicle offense investigators, experienced general investigators (i.e., investigators with no
specialized training in vehicle crime investigation), novice general investigators, and naive
participants with offense information relating to 30 offenses committed by 10 known offend-
ers (3 offenses each). The participants were asked to review the offense information and
determine which of the offenses were linked. They found that investigators were significantly
more accurate than naive participants, but there were no differences in accuracy between dif-
ferent types of investigators (each group identified about half of the possible links correctly).
Most recently, Bennell, Bloomfield, Snook, Taylor, and Barnes (2010) examined how
university students, police professionals, and a logistic regression model performed on a
linking task. Information on 38 pairs of burglaries, some of which represented linked
crimes, was provided to each participant. Half of the participants in each group were pro-
vided with training that informed them that the likelihood of two offenses being committed
by the same offender increases as the distance between the offenses decreases (see Bennell
& Canter, 2002). Participants were asked to decide for each offense pair whether or not the
same offender committed the crimes. They found that students outperformed police profes-
sionals, that providing information about appropriate linking cues can increase accuracy
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significantly, but that statistical models tend to outperform human judgment. The major
problem for the participants, even in the trained condition, was an overreliance on ineffec-
tive linking cues, which seemed to result from inaccurate beliefs about what MO features
in burglary are consistent and/or distinctive.
Accepting that there are some issues with their external validity, these studies do not
provide strong evidence that various types of police professionals, including experienced
investigators, can link serial crimes accurately. If the studies just reviewed had shown
positive results, it would be reasonable to assume that trained linkage analysts would do as
well as the tested participants, if not better, since they have been trained in the linkage task.
Unfortunately, the reality is that we simply do not know at present whether trained linkage
analysts possess the ability to link serial crimes, either in laboratory-based studies or in
naturalistic settings where systems such as ViCLAS are used.
Another concern is that the poor performance of participants in linking studies raises the
possibility that the fallibility of human decision making, which is often found in other
decision-making domains (Jacob, Gaultney, & Salvendy, 1986; Kahneman, Slovic, &
Tversky, 1982; Kleinmuntz, 1990), may be a problem in the investigative domain too. If
this is true, trained linkage analysts may fare little better than the participants in these stud-
ies. What we know about how actual linking decisions are made in some operational set-
tings by trained analysts does little to ease our concerns. For example, we have been
informed that many trained linkage analysts rely on an experience-based, subjective, idio-
graphic approach for selecting linking cues rather than a data-driven, objective, nomothetic
approach (also see RCMP, n.d.). This does not accord well with the published decision-
making literature, which has historically highlighted the superiority of the latter approach
over the former (e.g., Grove & Meehl, 1996). Indeed, that literature suggests that (unaided)
linkage analysts may be ill equipped to perform well on the linking task, thus making it
difficult for them to achieve accuracy rates that could be achieved using more mechanical
(standardized) decision-making procedures.
Future research on issues of linking ability. No matter what emerges from any of the
other lines of research described above, the ultimate issue from an operational policing
perspective will be whether or not linkage analysts can establish links between crimes
accurately. Although it would be ideal to conduct field studies to examine linkage decision
accuracy, a more fruitful alternative, at least initially, may be to conduct laboratory tests
that use specific linkage systems. The studies described above (e.g., Bennell et al., 2010;
Canter et al., 1991; Santtila et al., 2004) provide one potential approach for conducting
such studies, and the degree of external validity associated with these studies could be
improved with the assistance of police organizations. The findings from such studies could
increase the degree of linking accuracy that can be achieved.
Some obvious questions for future research in this area might be the following: What
linking strategies are currently used by linkage analysts? What level of accuracy can be
achieved when using these strategies? How does this level of accuracy compare to the level
of accuracy achieved using other (e.g., actuarial) methods? Can the accuracy of linking
decisions be improved with the introduction of additional decision support tools or empir-
ically informed training? What factors (e.g., experience, training, motivation, pressure)
influence one’s ability to make accurate linking decisions?
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Beyond research examining the aforementioned assumptions, another major research
endeavor should be to establish the success rate (e.g., number of actual links established)
associated with the various linkage systems being used by police organizations. Although
we are aware of anecdotes of successful police investigations that have drawn on linkage
systems as part of their investigations, these anecdotes by themselves do not constitute
strong evidence in support of linkage systems. We are not aware of any data from wide-
scale studies that provide an indication of how successful existing linkage systems are in
assisting investigations or the role that linkage systems played in investigative successes.
This is despite the fact that some of these systems are meant to be updated when potential
links are confirmed or rejected by investigators.
Future research that establishes the effectiveness of linkage systems will be useful for at
least two reasons. First, it will provide developers of these systems, the analysts who use
them, and the investigators who depend on the results with evidence that the systems are in
fact effective and worth the cost (in terms of time, effort, and money). Second, this research
will provide a baseline with which to compare future adjustments to the coding framework,
the system itself, and the analysts using the system (e.g., with respect to training). We recom-
mend that this research go beyond an evaluation of potential links, for which some informa-
tion is already available. The real need is to establish the number of actual links achieved by
the system under investigation. Obtaining an accurate measure of system success requires
that investigators furnished with a potential link provide feedback on whether or not the
crimes were actually linked. Getting such feedback from time-constrained investigators will
be challenging, but actual links is clearly the best measure of a system’s success.
Our intention with this article was not to minimize the efforts of law enforcement per-
sonnel who have dedicated much time and energy to developing crime linkage systems, nor
was it our intention to criticize those analysts who work tirelessly to identify serial offend-
ers. It was our intention to examine critically the assumptions underlying crime linkage
systems, systems that are widely used around the world without being subjected to empiri-
cal scrutiny. Police agencies will have to decide for themselves how much weight to put on
the issues we raised in this article and what conclusions to draw regarding the potential
value of linkage systems. At the very least, we believe that these systems ought to be
evaluated as a matter of urgency because there exists a real risk that current linking efforts
are not achieving optimal results. We hope the research agenda described in this article, if
adopted by researchers, will go some way toward addressing the concerns raised in this
critical review and allow crime linkage systems (and the analysts who operate them) to
reach their full potential.
1. For example, the 38-page Violent Crime Linkage Analysis System booklet currently consists of 156 open-ended and
closed-ended questions that relate to a number of categories, such as victim, offender, and offense information. There is also
an e-version of this booklet that is now available.
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2. Of course, the value of any research that draws on data contained within linkage systems ultimately hinges on the
assumption of data accuracy as well. Exactly how accurate such data need to be to be useful for research or linking purposes
is a difficult question to answer, but the importance of data accuracy, in general terms, is surely something that everyone can
agree on.
3. Issues of consistency and distinctiveness are often examined in relation to property crimes, such as arson, burglary, and
vehicle theft, which are rarely included in linkage systems (e.g., Bennell & Canter, 2002; Bennell & Jones, 2005; Ewart,
Oatley, & Burn, 2005; Goodwill & Alison, 2006; Markson, Woodhams, & Bond, 2010; Santtila, Fritzon, & Tamelander, 2004;
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Craig Bennell is an associate professor of psychology at Carleton University and director of Carleton’s Police Research Lab.
Much of his research examines the reliability, validity, and usefulness of psychologically based investigative techniques,
including methods that are used to link serial crimes. His other stream of research examines factors that influence police
decision making in use-of-force encounters.
Brent Snook is an associate professor of psychology and director of the Bounded Rationality and the Law Laboratory at
Memorial University of Newfoundland. His research primarily involves ways of improving the criminal justice system,
which includes the study of decision making in legal settings, interviewing and interrogations, and pseudoscience in the
criminal justice system.
Sarah MacDonald is a PhD student at Memorial University of Newfoundland, Canada. She obtained her MSc at Memorial
University of Newfoundland in 2011 and her BSc (honours) at Dalhousie University in 2009. Her general research interests
include investigative interviewing practices and deception detection.
John C. House is a superintendent of the Royal Newfoundland Constabulary (RNC) in Canada. He holds an MSc in inves-
tigative psychology from the University of Surrey and presently directs the Criminal Investigation Division of the RNC. He
has an interest in the critical evaluation of approaches and methods used by police organizations, with a view that best prac-
tices are implemented.
Paul J. Taylor is senior lecturer (associate professor) in the Department of Psychology at Lancaster University, UK. He
directs the university’s Investigative Expertise Unit, a multidisciplinary research group that brings together expertise in
behavioral science and technology to address areas such as protective security, vulnerable witness interviewing, and the
investigation of terrorism.
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... There has been an increasing use of computerized record linkage (CRL) method in various studies such as historical cohort mortality studies, cancer studies, political studies and crime studies, in several countries, Howe (1985Howe ( , 1998, Bennell et al. (2012), Giraud-Carrier et al. (2015). With very little effort, the method enables us to collect a large amount of data by linking records of human exposure to environmental hazards with records on health status. ...
We consider the problem of predicting a function of misclassified binary variables. We make an interesting observation that the naive predictor, which ignores the misclassification errors, is unbiased even if the total misclassification error is high as long as the probabilities of false positives and false negatives are identical. Other than this case, the bias of the naive predictor depends on the misclassification distribution and the magnitude of the bias can be high in certain cases. We correct the bias of the naive predictor using a double sampling idea where both inaccurate and accurate measurements are taken on the binary variable for all the units of a sample drawn from the original data using a probability sampling scheme. Using this additional information and design-based sample survey theory, we derive a biascorrected predictor. We examine the cases where the new bias-corrected predictors can also improve over the naive predictor in terms of mean square error (MSE).
... Toutefois, des doutes sérieux pèsent aujourd'hui sur l'efficacité de ce genre de méthodes, en fonction des investissements qui sont consentis (Witzig 2003 ;Snook et al. 2008 ;Spinney 2010 ;Bennell et al. 2012). La publication de Witzig (2003) dans la revue du FBI a alimenté ce scepticisme. ...
Le rôle de la police scientifique est d’abord d’exploiter les traces laissées lors d’activités criminelles. Elle est aujourd’hui équipée de technologies de traçabilité si puissantes que celles-ci ont, en peu de temps, démultiplié la quantité et la variété de données mises à disposition de l’enquête judiciaire et du renseignement criminel. Or cette évolution rapide a paradoxalement eu pour conséquence une remise en question du rôle, du statut et de l’action de la police scientifique : qu’attend-on aujourd’hui de ces services ? Que sont-ils supposés conclure à partir de données devenues aussi considérables que spécialisées et fragmentées ? L’auteur décrit comment la police scientifique évolue vers une nouvelle discipline appelée « traçologie ». Celle-ci s’oppose à l’hyper-spécialisation en encourageant les professionnels à adopter une vision d’ensemble essentielle pour résoudre des enquêtes complexes, analyser la criminalité sérielle et renseigner l’action de sécurité. Un ouvrage manifeste, principalement destiné aux criminalistes et criminologues concernés par l’avenir de la police scientifique, mais aussi à tous les professionnels de la sécurité, qui trouveront dans ces pages des méthodes et des modèles directement applicables, aux étudiants en sciences criminelles, aux chercheurs en quête d’interdisciplinarité et au public intéressé par les méthodes d’investigation et curieux d’en découvrir les arcanes.
... Crime linkage studies are generally based on the similarity of criminal behaviour, which relies on three assumptions [25,26]: (1) The consistency of criminal behaviour and the fact that the same offender will not change much from crime to crime; (2) In criminal behaviour, different criminals display distinctive behaviours that are distinct from one another; (3) The criminal ...
... This has caused some to argue there are critical limitations to what can be inferred from analysis (Bennett- Thatcher, 2014). In particular, empirical research analyzing law enforcement data has shown that information stored on police records management systems (RMS) is riddled with challenges such as missing, incomplete (Sanders & Condon, 2017), and inaccurate data (Richardson et al., 2019), with the end product based on subjective decision-making (Bennell et al., 2012;Sanders & Condon, 2017). ...
Crime and Intelligence Analysis in Canada provides a comprehensive introduction to the twin fields of crime analysis and intelligence analysis from a Canadian perspective. Written for both students and practitioners in public law enforcement and corporate security, this resource examines analytical methods, information systems, technologies, and governance issues, with a particular focus on Canadian institutional practices and contexts.
... There are a number of factors that researchers should consider when it comes to evaluating how practitioners use these computerised databases to assist with the linkage process. These are summarised in Bennell et al. (2012) review of such linkage systems, and in Davies et al.'s (2020a) updated review of ViCLAS usage. These authors note that (as well as the assumptions of consistency and distinctiveness being valid) the data entered into such systems need to be reliable and accurate, that practitioners should be able to accurately conduct linkage using these systems, and that the design of such systems must be fit for purpose. ...
Crime linkage can be a useful tool in the investigation of sexual offenses when other, physical evidence is unavailable or too costly to process. It involves identifying behavior that is both consistent and distinctive, and thus forms an identifiable pattern through which a series of offenses committed by the same offender can be distinguished. While there is a substantial body of research to support the principles of crime linkage, samples often contain only one type of sexual offense, and further research is needed into offenses such as voyeurism and exhibitionism. In practice, there are a number of ways in which crime linkage can be conducted, and a variety of terms are used to describe these different processes. While writings from practitioners provide insight into how crime linkage is conducted, research now needs to focus more on systematically mapping its practice and documenting procedural differences. There are also a number of additional considerations that require further research attention where the practice of crime linkage is concerned, such as the utility of computerised databases designed to assist with the process, the human decision-making element of linking and how bias can affect this, and the effects of expertise and training on linkage efficacy.
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E tanulmányban arra a kérdésre keressük a választ, mivel tehető könnyebbé, biztosabbá, megbízhatóbbá a bűncselekmények összekapcsolása. Az egyik megoldást a profilalkotással, konzisztenciával kapcsolatos kutatások eredményei jelenthetik, másik oldalról pedig az elemző- értékelő munka igénybevétele, szoftveres támogatása és kutatásokra támaszkodó fejlesztése. Minél megbízhatóbb kutatási eredményeket tudnak alapul venni a rendvédelmi szervek és az elemző egységek, annál nagyobb hatékonysággal végezhetik munkájukat a sorozatjelleg megállapításakor és vizsgálatakor. Tanulmányunkban áttekintjük a bűncselekmények összekapcsolásával kapcsolatos legfontosabb kutatási eredményeket, valamint betekintést nyújtunk gyakorlati bevezetésük lehetőségeibe. Publikációnk végén pedig felvetünk néhány lehetséges kutatási témát, amelyekkel modernizálható lenne a hazai elemző-értékelő tevékenység, illetve az elektronikus Modus Operandi Nyilvántartás.
Despite contemporary media portrayals, violent crime has continued to decrease in recent decades. Consistent with traditional types of violent crime (e.g., homicide), serial homicide has also continued to decrease. Although the methods of investigation for traditional violent crime have been examined thoroughly, research specific to serial homicide is scarce. In a study of 671 serial homicide perpetrators, we examined the timeline of each investigation and identified the methods used by law enforcement to identify, and sometimes apprehend, serial killers. Overall, there were 22 distinct methods of investigation. The most common methods were victim survived, DNA, turned in by an associate, family, or friend, fingerprints, prior offending history, body found in home, and being arrested for an unrelated charge. This study also describes how methods of investigation vary over time and trends across decades. Implications of the findings are discussed.
In the decade since the publication of the first edition of The Cambridge Handbook of Forensic Psychology, the field has expanded into areas such as social work and education, while maintaining the interest of criminal justice researchers and policy makers. This new edition provides cutting-edge and comprehensive coverage of the key theoretical perspectives, assessment methods, and interventions in forensic psychology. The chapters address substantive topics such as acquisitive crime, domestic violence, mass murder, and sexual violence, while also exploring emerging areas of research such as the expansion of cybercrime, particularly child sexual exploitation, as well as aspects of terrorism and radicalisation. Reflecting the global reach of forensic psychology and its wide range of perspectives, the international team of contributors emphasise diversity and cross-reference between adults, adolescents, and children to deliver a contemporary picture of the discipline.
Investigative Psychology (IP) as an empirical field of study that focusses on the psychological input to the full range of issues that relate to the investigation of crime. IP focusses on three overall processes present in any investigation that can be improved by psychological study; 1) Retrieving information from the crime scene for the purpose of analysis and research; 2) Making decisions during criminal investigations; and 3) Analysing criminal behaviour. For this last component, three general interlinked areas have been the focus of research: individual differentiation which aims to establish differences between the behavioral actions of offenders and identify subgroups of crime scene types; behavioural consistency which aims to understand an offender’s behavioural consistency across a series of crimes; and inferences about offender characteristics, which aims to establish the nature of the consistency between the most likely characteristics of an offender based on the way an offender acts at the time of the crime, and is at the core of offender profiling.
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Little is known about the stability of modus operandi (MO) in sexual offending. The authors studied a cohort of all sexual offenders released from prison into the Swedish community during the years from 1993 to 1997 (N = 1,303) and analyzed sexual reoffenders’ MO in terms of victim choice, offense nature, and severity, comparing prior offenses with those registered during an average 6-year follow-up. Stability in MO, explored with Cohen’s Kappa and Odds Ratios (ORs) as measures of agreement across registered sexual offenses, was high, specifically with respect to victim choice. Results are discussed in relation to sexual deviance and opportunity structure. The authors argue that assessment and management of sexual recidivism risk might benefit from information on offense MO. Furthermore, the results could inform police investigative strategies, such as linking multiple offenses committed by an unidentified offender.
Many decisions are based on beliefs concerning the likelihood of uncertain events such as the outcome of an election, the guilt of a defendant, or the future value of the dollar. Occasionally, beliefs concerning uncertain events are expressed in numerical form as odds or subjective probabilities. In general, the heuristics are quite useful, but sometimes they lead to severe and systematic errors. The subjective assessment of probability resembles the subjective assessment of physical quantities such as distance or size. These judgments are all based on data of limited validity, which are processed according to heuristic rules. However, the reliance on this rule leads to systematic errors in the estimation of distance. This chapter describes three heuristics that are employed in making judgments under uncertainty. The first is representativeness, which is usually employed when people are asked to judge the probability that an object or event belongs to a class or event. The second is the availability of instances or scenarios, which is often employed when people are asked to assess the frequency of a class or the plausibility of a particular development, and the third is adjustment from an anchor, which is usually employed in numerical prediction when a relevant value is available.
Psychological profiling represents the investigative technique of analyzing crime behaviors for the identification of probable offender characteristics. Profiling has progressively been incorporated into police procedures despite a surprising lack of empirical research to support its validity. Indeed, in the study of sexual murder for the purpose of profiling, very few quantitative, academically reviewed studies exist. This article reports on the results of a 4- year study into Australian sexual murders for the development of psychological profiling. The study involved 85 cases of sexual murder sampled from all Australian police jurisdictions. The statistical procedure of multidimensional scaling was employed. This analysis produced a five-cluster model of sexual murder behavior. First, a central cluster of behaviors was identified that represents common behaviors to all patterns of sexual murder. Next, four distinct out- lying patterns—predator, fury, perversion, and rape—were identified that each demonstrated distinct offence styles. Further analysis of these patterns also identified distinct offender characteristics that allow for the use of empirically robust offender profiles in future sexual murder investigations.
People exhibit coherent patterns of experience and action that cannot be fully described or explained by personality trait models. Rather, personality coherence is expressed in dispositional tendencies that violate the structure of common trait categories. Across contexts, people display predictable patterns of behavioral variation that cannot be captured by trait constructs, which correspond to mean levels of response. In addition to these empirical findings, theoretical work in both psychology and philosophy challenges the conceptual strategies through which trait models explain personality coherence. These empirical and theoretical points can be addressed by alternative theoretical models that specify how underlying psychological systems give rise to both common and idiosyncratic patterns of personality consistency and variability.