http://cdp.sagepub.com/ScienceCurrent Directions in Psychological http://cdp.sagepub.com/content/15/3/113The online version of this article can be found at: DOI: 10.1111/j.0963-7214.2006.00418.x 2006 15: 113Current Directions in Psychological ScienceRobert F. Krueger and Kristian E. Markonto Develop an Empirically Based ModelUnderstanding Psychopathology : Melding Behavior Genetics, Personality, and Quantitative Psychology Published by: http://www.sagepublications.comOn behalf of: Association for Psychological Science can be found at:Current Directions in Psychological ScienceAdditional services and information for http://cdp.sagepub.com/cgi/alertsEmail Alerts: http://cdp.sagepub.com/subscriptionsSubscriptions: http://www.sagepub.com/journalsReprints.navReprints: http://www.sagepub.com/journalsPermissions.navPermissions: at UNIV OF COLORADO LIBRARIES on August 24, 2011cdp.sagepub.comDownloaded fromUnderstanding PsychopathologyMelding Behavior Genetics, Personality, and QuantitativePsychology to Develop an Empirically Based ModelRobert F. Krueger and Kristian E. MarkonUniversity of MinnesotaABSTRACT—Research on psychopathology is at a historicalcrossroads. New technologies offer the promise of lastingadvances in our understanding of the causes of humanpsychological suffering. Making the best use of these tech-nologies, however, requires an empirically accurate modelof psychopathology. Much current research is framed bythe model of psychopathology portrayed in current ver-sions of the Diagnostic and Statistical Manual of MentalDisorders (DSM; American Psychiatric Association, 2000).Although the modern DSMs have been fundamental inadvancing psychopathology research, recent research alsochallenges some assumptions made in the DSM—for ex-ample, the assumption that all forms of psychopathologyare well conceived of as discrete categories. Psychologicalscience has a critical role to play in working through theimplications of this research and the challenges it presents.In particular, behavior-genetic, personality, and quanti-tative-psychological research perspectives can be meldedto inform the development of an empirically based modelof psychopathology that would constitute an evolutionof the DSM.KEYWORDS—classification; DSM; statistics; com orbidity;dimensions; categoriesPsychopathology rese arch is at a historical crossroads. Powerfultechnologies, such as molec ular genetics and sophisticatedstatistical models, now exist to aid us in our attempts to under-stand the origins of psychological suffering. To fully exploit thesetechnologies, however, we need to know how to best conceptu-alize psychopathol ogy. We need an empirically based model ofpsychopathology that can guide our inquiries into its origins.Most psychopathology research is currently framed by thesystem provided in the fourth edition (text revision) of the Di-agnostic and Statistical Manual of Mental Disorders (DSM-IV-TR;American Psychiatric Association, 2000). A number of specificassumptions underlie the classification of all disorders describedin the DSM-IV-TR. A cardinal assumption is that mental disor-ders are categorical: The manual lists a large number of cate-gories of mental disorder, and for each category, a series ofcriteria for category membership are listed. People are assumedto be either members of these categories or nonmembers; gradeddegrees of category membership are not permitted. Importantly,the DSM-IV-TR itself acknowledges potential limitations of thiscategorical approach to conceptualizing psychopathology, notingthat ‘‘a categorical approach to classification works best when allmembers of a diagnostic class are homogenous, when there areclear boundaries between classes, and when the different classesare mutually exclusive’’ (p. xxxi).Each of these areas has proven problematic for DSM catego-ries. Members of specific diagnostic classes tend to be hetero-geneous, boundaries between classes are often unclear, andclasses are rarely mutually exclusive. This is the sense in whichpsychopathology research is at a historical crossroads. DSM-defined categories are the most frequent targets of psychopath-ological inquiry, yet reliance on DSM-defined categories oftenresults in significant problems in research design and inter-pretation. To pick a specific example for illustrative purposes, ifone wants to understand depression, what should be done aboutthe fact that the boundary between depression and other DSMcategories is often unclear (e.g., depression overlaps with dys-thymia; Klein & Santiago, 2003) and many people who meetcriteria for depression meet criteria for other disorders as well(e.g., anxiety disorders; Kessler, DuPont, Berglund, & Wittchen,1999)? Is it possible to develop an empirically based approachto psychopathology that could overcome these limitations?The development of such a system is a tract able goal, and thepursuit of this goal involves integrating a number of areas ofinquiry that represent quintessential strengths of psychologicalscience. Some broad outlines of such a system can be seen bytying together recent research findings from these areas:Specifically, research strategies, concepts, and findings fromAddress correspondence to Robert F. Krueger, Department of Psy-chology, University of Minnesota, Elliott Hall, 75 E. River Rd.,Minneapolis, MN 55455; e-mail: [email protected] DIRECTIONS IN PSYCHOLOGICAL SCIENCEVolume 15—Number 3 113Copyright r 2006 Association for Psychological Science at UNIV OF COLORADO LIBRARIES on August 24, 2011cdp.sagepub.comDownloaded fromquantitative psychology, behavior genetics, and personalitypsychology provide the tools needed to develop an empiricallybased model of psychopathology.CONTRIBUTIONS OF QUANTITATIVE PSYCHOLOGYTO UNDERSTANDING PSYCHOPATHOLOGYOne prominent movement in psychology during recent decadeshas been the use of explicit quantitative models to describe andpredict psychological phenomena. Quantitative models are setsof mathematical and statistical equations describing and pre-dicting psychological phenomena. Structural-equation models,item-response models, growth-curve models, and other latent-variable models have allowed tremendous increases in the so-phistication of theories that can be tested and in the confidenceof our conclusions about those theo ries. These methods also holdpromise for understanding psychopathology, because they allowempirical comparison of different classification