'''Trækteori''' (efter engelsk: ''trait theory'') går helt essentielt ud på, at finde og klassificere nogle træk ved menneskers personlighed. 

Når man i praksis undersøger en persons personlighed i forbindelse med en trækteori foregår det ved at personen selv udfylder et større spørgeskema. Svarene vægtes derefter således at man kan uddrage nogle generelle trœk, f.eks. graden af "udadvendthed".

Der findes en rœkke forskellige spørgeskemaer og psykologen Hans Jürgen Eysenck har været en af pionerene indenfor feltet. 

== Fem-faktormodellen ==
Paul T. Costa, Jr. og Robert R. McCrae er ophavsmændene bag det måske mest berømte forsøg på at gøre dette. Deres fem-faktor model (eller "the big five) er netop et bud på dette, og går ud på, at et hvert individ placerer sig på forskellige steder i forhold til "at have" mere eller mindre af fem karaktertræk. Hvert af disse træk kan yderligere deles op i seks ''facetter''<ref>Paul T. Costa, Jr og Robert R. McCrae, ''NEO PI-R Manual'', PsykologiErhverv, Virum, 2003. Oversat og bearbejdet af Henrik Skovdahl Hansen og Erik Lykke Mortensen.</ref>:
# Neuroticisme: Negativ affektivitet vs. Emotional stabilitet. Facetter: Angst, irritabilitet, depression, jeg-bevidsthed, impulsivitet, sårbarhed.
# varme, selskabstrang, dominans, aktivitet, spændingssøgen og "positive emotioner"
# Åbenhed overfor oplevelser: intellekt, kultur, vs. lukkethed. Facetter: Fantasi, æstetisk sans, "følelser", "handlinger", "ideer" og "værdier".
# Venlighed (engelsk: ''agreeableness''): venlig, "compliance", socialiserbar vs. antagonisme. Facetter: Tillidsfuldhed, ligefremhed, altruisme, efterrettelighed, beskedenhed og blødsødenhed
# Samvittighedsfuldhed (engelsk: ''conscientiousness''): omhyggelighed, vilje til at opnå noget, rettethed vs. Ikke at være rettet mod noget. Facetter: kompetence, orden, pligtopfyldenhed, præstationsorientering, selvdisciplin og besingdighed.

Der er udviklet et spørgeskema/test (NEO PI-R) der estimerer disse fem faktorer, og i dette spørgeskema er hver af disse fem faktorer  yderligere opdelt i 6 såkaldte "facetter".
Spørgeskemaet bruges indenfor forskning og som et erhvervspsykologiske værktøj f.eks. i forbindelse med ansættelser.
Firmaet ''Psychological Assessment Resources'' sælger en engelsk version af spørgeskemaet, og det findes også i en dansk version.

In personality. Trait theorists are primarily interested in the measurement of ''traits'', which can be defined as habitual patterns of behavior, thought, and emotion.<ref>Saul Kassin, (2003). ''Psychology''. USA: Prentice-Hall, Inc.</ref> According to this perspective, traits are relatively stable over time, differ among individuals (e.g. some people are outgoing whereas others are shy), and influence behavior.

Gordon Allport was an early pioneer in the study of traits, which he sometimes referred to as dispositions. In his approach, ''central traits'' are basic to an individual's personality, whereas ''secondary traits'' are more peripheral. ''Common traits'' are those recognized within a culture and may vary between cultures. ''Cardinal traits'' are those by which an individual may be strongly recognized. Since Allport's time, trait theorists have focused more on group statistics than on single individuals. Allport called these two emphases "nomothetic" and "idiographic," respectively.

There is a nearly unlimited number of potential traits that could be used to describe personality. The statistical technique of factor analysis, however, has demonstrated that particular clusters of traits reliably correlate together. Hans Eysenck has suggested that personality is reducible to three major traits.<ref>Hans Eysenck, (1967). ''The biological basis of personality.'' Springfield, IL: Thomas.</ref> <ref>Hans Eysenck, (1991). Dimensions of personality: 16: 5 or 3? Criteria for a taxonomic paradigm. ''Personality and Individual Differences'', ''12'', 773-90.</ref> Other researchers argue that more factors are needed to adequately describe human personality.<ref>Saucier, G., & Goldberg, L. R. (1998). What is beyond the Big Five? ''Journal of Personality'', ''66'', 495–524.</ref> Many psychologists currently believe that five factors are sufficient.<ref>McCrae, R. R., & Costa, P. C., Jr. (1987). Validation of the five-factor model across instruments and observers. ''Journal of Personality and Social Psychology'', ''52'', 81–90.</ref> <ref>Costa, P. T., & McCrae, R. R. (1992). Four ways five factors are basic. ''Personality and Individual Differences'', ''13'', 653-665.</ref>

Virtually all trait models, and even ancient Greek philosophy, include extraversion vs. introversion as a central dimension of human personality. Another prominent trait that is found in nearly all models is Neuroticism, or emotional instability.

==Two taxonomies==
Eysenck's three factor model contains the traits of extraversion, neuroticism, and psychoticism. The five factor model contains openness, extraversion, neuroticism, agreeableness, and conscientiousness. These traits are the highest-level factors of a hierarchical taxonomy based on the statistical technique of factor analysis. This method produces factors that are continuous, bipolar, can be distinguished from temporary states, and can describe individual differences.<ref>Goldberg, L. R. (1993). The structure of phenotypic personality traits. ''American Psychologist'', ''48'', 26–34.</ref> Both approaches extensively use self-report questionnaires. The factors are intended to be orthogonal (uncorrelated),<ref>Hans Eysenck, (1990). Biological dimensions of personality. In L. A. Pervin (Ed.), ''Handbook of personality: Theory and research'' (pp. 244-276). New York: Guilford.</ref> though there are often small positive correlations between factors. The five factor model in particular has been criticized for losing the orthogonal structure between factors.<ref>Block, J. (1995). A contrarian view of the five-factor approach to personality description. ''Psychological Bulletin'', ''117'', 187–215.</ref> <ref>Draycott, S. G., & Kline, P. (1995). The Big Three or the Big Five - the EPQ-R vs the NEO-PI: a research note, replication and elaboration. ''Personality and Individual Differences'', ''18'', 801-804.</ref> Hans Eysenck has argued that fewer factors are superior to a larger number of partly related ones.<ref>Eysenck, H. J. (1992). A reply to Costa and McCrae. P or A and C: The role of theory. ''Personality and Individual Differences'', ''13'', 867-868.</ref> Although these two approaches are comparable because of the use of factor analysis to construct hierarchical taxonomies, they differ in the organization and number of factors.

Whatever the causes, however, psychoticism marks the two approaches apart as the five factor model contains no such trait. Moreover, apart from simply being a different high-level factor psychoticism, unlike any of the other factors in either approach, does not fit a normal distribution curve. Indeed, scores are rarely high thus skewing a normal distribution. <ref>Matthews, G., Deary, I.J., & Whiteman, M.C. (2003).  ''Personality traits'' (2nd edition). Cambridge: Cambridge University Press.</ref>However, when they are high there is considerable overlap with psychiatric conditions such as antisocial and schizoid personality disorders. Similarly, high scorers on neuroticism are more susceptible to sleep and psychosomatic disorders.<ref>Hans Eysenck and S. B. G. Eysenck. (1991). The Eysenck Personality Questionnaire-Revised. Sevenoaks: Hodder & Stoughton.</ref> Five factor approaches can also predict future mental disorders,<ref>Costa, P. T., & McCrae, R. R. (1990). Personality disorders and the five factor model of personality. ''Journal of Personality Disorders'', ''4'', 362-371.</ref> <ref>Lynam, D. R., Caspi, A., Moffitt, T. E., Raine, A., Loeber, R., & Stouthamer-Loeber, M. (2005). Adolescent psychopathy and the Big Five: Results from two samples. ''Journal of Abnormal Child Psychology'', ''33'', 431-443.</ref>

==Lower order factors==
thumb|right|250px|Similarities between lower order factors for psychoticism and the factors of openness, agreeableness, and conscientiousness (from Matthews, Deary & Whiteman, 2003)