In psychology, trait theory (also called dispositional theory) is an approach to the study of human personality. Trait theorists are primarily interested in the measurement of traits, which can be defined as habitual patterns of behavior, thought, and emotion. According to this perspective, traits are relatively stable over time, differ across individuals (e.g. some people are outgoing whereas others are shy), and influence behavior. Traits are in contrast to states which are more transitory dispositions.
In some theories and systems, traits are something a person either has or does not have, but in many others traits are dimensions such as extraversion vs. introversion, with each person rating somewhere along this spectrum.
Gordon Allport was an early pioneer in the study of traits, which he also referred to as dispositions. In his approach, "cardinal" traits are those that dominate and shape a person's behavior; their ruling passions/obsessions, such as a need for money, fame etc. By contrast, "central" traits such as honesty are characteristics found in some degree in every person - and finally "secondary" traits are those seen only in certain circumstances (such as particular likes or dislikes that a very close friend may know), which are included to provide a complete picture of human complexity.
A wide variety of alternative theories and scales were later developed, including:
- Raymond Cattell's 16PF Questionnaire
- J. P. Guilford's Structure of Intellect
- Henry Murray's System of Needs
- Timothy Leary's Interpersonal circumplex
- Myers–Briggs Type Indicator
- Gray's Biopsychological theory of personality
Currently, two general approaches are the most popular:
- Eysenck Personality Questionnaire, (EPQ) ("the three-factor model"). Using factor analysis Hans Eysenck suggested that personality is reducible to three major traits: neuroticism, extraversion, and psychoticism.
- Big Five personality traits, ("the five-factor model"). Many psychologists currently believe that five factors are sufficient: neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness.
Comparing EPQ and Big FiveEdit
Testing methodology, and factorsEdit
Both the EPQ and Big Five approaches extensively use self-report questionnaires. The factors are intended to be orthogonal (uncorrelated), 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. Hans Eysenck has argued that fewer factors are superior to a larger number of partly related ones. 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, 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. 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. Five factor approaches can also predict future mental disorders.
There are two higher-order factors that both taxonomies clearly share: extraversion and neuroticism. Both approaches broadly accept that extraversion is associated with sociability and positive affect, whereas neuroticism is associated with emotional instability and negative affect.
Many lower-order factors, or facets, are similar between the two taxonomies. For instance, both approaches contain factors for sociability/gregariousness, for activity levels, and for assertiveness within the higher order factor extraversion. However, there are differences too. First, the three-factor approach contains nine lower-order factors and the five-factor approach has six.
Eysenck's psychoticism factor incorporates some of the polar opposites of the lower order factors of openness, agreeableness and conscientiousness. A high scorer on tough-mindedness in psychoticism would score low on tender-mindedness in agreeableness. Most of the differences between the taxonomies stem from the three factor model's emphasis on fewer high-order factors.
Although both major trait models are descriptive, only the three-factor model offers a detailed causal explanation. Eysenck suggests that different personality traits are caused by the properties of the brain, which themselves are the result of genetic factors. In particular, the three-factor model identifies the reticular system and the limbic system in the brain as key components that mediate cortical arousal and emotional responses respectively. Eysenck advocates that extraverts have low levels of cortical arousal and introverts have high levels, leading extraverts to seek out more stimulation from socializing and being venturesome. Moreover, Eysenck surmised that there would be an optimal level of arousal, after which inhibition would occur and that this would be different for each person.
In a similar vein, the three-factor approach theorizes that neuroticism is mediated by levels of arousal in the limbic system and that individual differences arise because of variable activation thresholds between people. Therefore, highly neurotic people when presented with minor stressors, will exceed this threshold, whereas people low in neuroticism will not exceed normal activation levels, even when presented with large stressors. By contrast, proponents of the five-factor approach assume a role of genetics and environment but offer no explicit causal explanation.
Given this emphasis on biology in the three-factor approach, it would be expected that the third trait, psychoticism, would have a similar explanation. However, the causal properties of this state are not well defined. Eysenck has suggested that psychoticism is related to testosterone levels and is an inverse function of the serotonergic system, but he later revised this, linking it instead to the dopaminergic system.
List of personality traitsEdit
|Openness to experience||Composed of two related but separable traits, Openness to Experience and Intellect. Behavioral aspects include having wide interests, and being imaginative and insightful, correlated with activity in the dorsolateral prefrontal cortex. Considered primarily a cognitive trait.|
|Conscientiousness||Scrupulous, meticulous, principled behavior guided or conforming to one's own conscience. Associated with the dorsolateral prefrontal cortex. Anorexics are noted to have higher levels of conscientiousness.|
|Extraversion||Gregarious, outgoing, sociable, projecting one's personality outward. The opposite of extraversion is introversion. Extraversion has shown to share certain genetic markers with substance abuse. Extraversion is associated with various regions of the prefrontal cortex and the amygdala.|
|Agreeableness||Refers to a compliant, trusting, empathic, sympathetic, friendly and cooperative nature.|
|Neuroticism||"Refers to an individual's tendency to become upset or emotional" (Hans Eysenck) "Neuroticism is the major factor of personality pathology" (Eysenck & Eysenck, 1969). Neuroticism has been linked to serotonin transporter (5-HTT) binding sites in the thalamus: as well as activity in the insular cortex. Neuroticism also predicts the occurrence of more negative life experiences.|
|Honesty-Humility||Tendency towards sincerity, modesty, fairness, and greed avoidance. Those who score high on this trait feel little desire to manipulate others or to break the rules for personal gain. Negatively correlated with the Dark triad.|
|Self-esteem (low)||A "favorable or unfavorable attitude toward the self" (Rosenberg, 1965). An individual's sense of his or her value or worth, or the extent to which a person values, approves of, appreciates, prizes, or likes him or herself" (Blascovich & Tomaka, 1991).|
|Harm avoidance||A tendency towards shyness, being fearful and uncertain, tendency to worry. Neonatal complications such as preterm birth have been shown to affect harm avoidance. People affected by eating disorders exhibit high levels of harm avoidance. The volume of the left amygdala in girls was correlated to levels of HA, in separate studies HA was correlated with reduced grey matter volume in the orbitofrontal, occipital and parietal regions.|
|Novelty seeking||Impulsive, exploratory, fickle, excitable, quick-tempered, and extravagant. Associated with addictive behavior.|
|Sensory processing sensitivity (SPS)||The defining trait of highly sensitive persons, characterized by the increased depth of processing of sensory input that underlies HSPs' greater proclivity to overstimulation, emotional reactivity and empathy, and sensitivity to stimuli.|
|Perfectionism||"I don't think needing to be perfect is in any way adaptive" (Paul Hewitt, PhD)
Socially prescribed perfectionism – "believing that others will value you only if you are perfect."
Self-oriented perfectionism – "an internally motivated desire to be perfect."
|Alexithymia||The inability to express emotions. "To have no words for one's inner experience" (Rený J. Muller PhD). In studies done with stroke patients, alexithymia was found to be more prevalent in those who developed lesions in the right hemisphere following a cerebral infarction. There is a positive association with post-traumatic stress disorder (PTSD), childhood abuse and neglect and alexithymia. Utilizing psychometric testing and fMRI, studies showed positive response in the insula, posterior cingulate cortex (PCC), and thalamus.|
|Rigidity||Inflexibility, difficulty making transitions, adherence to set patterns. Mental rigidity arises out of a deficit of the executive functions. Originally termed frontal lobe syndrome it is also referred to as dysexecutive syndrome and usually occurs as a result of damage to the frontal lobe. This may be due to physical damage, disease (such as Huntington's disease) or a hypoxic or anoxic insult.|
|Impulsivity||Risk taking, lack of planning, and making up one's mind quickly (Eysenck and Eysenck). A component of disinhibition. Abnormal patterns of impulsivity have been linked to lesions in the right inferior frontal gyrus and in studies done by Antonio Damasio author of Descartes Error, damage to the ventromedial prefrontal cortex has been shown to cause a defect in real-life decision making in individuals with otherwise normal intellect. Those who sustain this type of damage are oblivious to the future consequences of their actions and live in the here and now.|
|Disinhibition||Behavioral disinhibition is an inability or unwillingness to constrain impulses, it is a key component of executive functioning. Researchers have emphasized poor behavioral inhibition as the central impairment of ADHD. It may be symptomatic of orbitofrontal lobe syndrome, a subtype of frontal lobe syndrome which may be an acquired disorder as a result of traumatic brain injury, hypoxic ischemic encephalopathy (HIE), anoxic encephalopathy, degenerative diseases such as Parkinson's, bacterial or viral infections such as Lyme disease and neurosyphilis. Disinhibition has been consistently associated with substance abuse disorders, obesity, higher BMI, excessive eating, an increased rate of eating, and perceived hunger.|
|Psychoticism||Psychoticism is a personality pattern typified by aggressiveness and interpersonal hostility, one of four traits in Hans Eysenck's model of personality. High levels of this trait were believed by Eysenck to be linked to increased vulnerability to psychosis such as schizophrenia. He also believed that blood relatives of psychotics would show high levels of this trait, suggesting a genetic basis to the trait.|
|Obsessionality||Persistent, often unwelcome, and frequently disturbing ideas, thoughts, images or emotions, rumination, often inducing an anxious state. Obsessionality may result as a dysfunction of the basal ganglia.|
- Saul Kassin, (2003). Psychology. USA: Prentice-Hall, Inc.
- Hans Eysenck, (1967). The biological basis of personality. Springfield, IL: Thomas.
- Eysenck, Hans (1991). "Dimensions of personality: 16: 5 or 3? Criteria for a taxonomic paradigm". Personality and Individual Differences. 12: 773–790. doi:10.1016/0191-8869(91)90144-z.
- 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. doi:10.1037/0022-3518.104.22.168. PMID 3820081.
- Costa, P. T.; McCrae, R. R. (1992). "Four ways five factors are basic". Personality and Individual Differences. 13: 653–665. doi:10.1016/0191-8869(92)90236-i.
- Hans Eysenck, (1990). Biological dimensions of personality. In L. A. Pervin (Ed.), Handbook of personality: Theory and research (pp. 244–276). New York: Guilford.
- Block, J (1995). "A contrarian view of the five-factor approach to personality description". Psychological Bulletin. 117: 187–215. doi:10.1037/0033-2909.117.2.187. PMID 7724687.
- 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. doi:10.1016/0191-8869(95)00010-4.
- 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. doi:10.1016/0191-8869(92)90003-8.
- Matthews, G., Deary, I.J., & Whiteman, M.C. (2003). Personality traits (2nd edition). Cambridge: Cambridge University Press.
- Hans Eysenck and S. B. G. Eysenck. (1991). The Eysenck Personality Questionnaire-Revised. Sevenoaks: Hodder & Stoughton.
- Costa, P. T.; McCrae, R. R. (1990). "Personality disorders and the five factor model of personality". Journal of Personality Disorders. 4: 362–371. doi:10.1521/pedi.1922.214.171.1242.
- 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. doi:10.1007/s10648-005-5724-0.
- Eysenck, H. J., & Eysenck, M. W. (1985). Personality and individual differences: A natural science approach. New York: Plenum.
- Eysenck, H.J. (1967). The biological basis of personality. Springfield, IL: Thomas.
- Eysenck, H. J. (1994). "Creativity and personality: Word association, origence, and Psychoticism". Creativity Research Journal. 7: 209–216. doi:10.1080/10400419409534525.
- Jeronimus, B.F.; Riese, H.; Sanderman, R.; Ormel, J. (2014). "Mutual Reinforcement Between Neuroticism and Life Experiences: A Five-Wave, 16-Year Study to Test Reciprocal Causation". Journal of Personality and Social Psychology. 107 (4): 751–64. doi:10.1037/a0037009. PMID 25111305.
- Eysenck, H. J. (1992). "The definition and measurement of psychoticism". Personality and Individual Differences. 13: 757–785. doi:10.1016/0191-8869(92)90050-y.
- Eysenck, H. J. (1997). "Personality and experimental psychology: The unification of psychology and the possibility of a paradigm". Journal of Personality and Social Psychology. 73: 1224–1237. doi:10.1037/0022-35126.96.36.1994.
- DeYoung, CG; Peterson, JB; Higgins, DM (Aug 2005). "Sources of openness/intellect: cognitive and neuropsychological correlates of the fifth factor of personality". J Pers. 73 (4): 825–58. doi:10.1111/j.1467-6494.2005.00330.x. PMID 15958136.
- MacLaren, VV; Best, LA (Aug 2009). "Female students' disordered eating and the big five personality facets". Eat Behav. 10 (3): 192–5. doi:10.1016/j.eatbeh.2009.04.001. PMID 19665103.
- Heaven, PC; Mulligan, K; Merrilees, R; Woods, T; Fairooz, Y (Sep 2001). "Neuroticism and conscientiousness as predictors of emotional, external, and restrained eating behaviors". Int J Eat Disord. 30 (2): 161–6. doi:10.1002/eat.1068. PMID 11449449.
- Casper, RC; Hedeker, D; McClough, JF (Sep 1992). "Personality dimensions in eating disorders and their relevance for subtyping". J Am Acad Child Adolesc Psychiatry. 31 (5): 830–40. doi:10.1097/00004583-199209000-00008. PMID 1400113.
- Luo, X; Kranzler, HR; Zuo, L; Wang, S; Gelernter, J (2007). "Personality Traits of Agreeableness and Extraversion are Associated with ADH4 Variation". Biol Psychiatry. 61 (5): 599–608. doi:10.1016/j.biopsych.2006.05.017. PMC . PMID 17069770.
- Wright, CI.; et al. (Dec 2006). "Neuroanatomical correlates of extraversion and neuroticism". Cereb Cortex. 16 (12): 1809–19. doi:10.1093/cercor/bhj118. PMID 16421327.
- Mendez, MF; Chen, AK; Shapira, JS; Lu, PH; Miller, BL (2006). "Acquired extroversion associated with bitemporal variant of frontotemporal dementia". J Neuropsychiatry Clin Neurosci. 18 (1): 100–7. doi:10.1176/appi.neuropsych.18.1.100. PMID 16525077.
- Rankin, KP.; et al. (2004). "Right and left medial orbitofrontal volumes show an opposite relationship to agreeableness in FTD". Dement Geriatr Cogn Disord. 17 (4): 328–32. doi:10.1159/000077165. PMC . PMID 15178947.
- Graziano, WG; Tobin, RM.; et al. (Jun 1993). "Genetic and environmental effects on openness to experience, agreeableness, and conscientiousness: an adoption/twin study". J Pers. 61 (2): 159–79. PMID 8345444.
- Graziano, WG; Tobin, RM (October 2002). "Agreeableness: dimension of personality or social desirability artifact?". J Pers. 70: 695–727. PMID 12322857.
- Miller, JL; et al. (Jan 2006). "Neuroticism and introversion: a risky combination for disordered eating among a non-clinical sample of undergraduate women". Eat Behav. 7 (1): 69–78. doi:10.1016/j.eatbeh.2005.07.003. PMID 16360625.
- Takano, A; et al. (Sep 2007). "Relationship between neuroticism personality trait and serotonin transporter binding". Biol Psychiatry. 62 (6): 588–92. doi:10.1016/j.biopsych.2006.11.007. PMID 17336939.
- Deckersbach, T; et al. (2006). "Regional cerebral brain metabolism correlates of neuroticism and extraversion". Depress Anxiety. 23 (3): 133–8. doi:10.1002/da.20152. PMID 16470804.
- Button EJ Self-esteem, eating problems and psychological wellbeing in a cohort of school age 15–16: question and interview PMID 8986516 Int J Eat Disord 1997 Jan;21(1):39–41
- Strober, M (1983). "Personality factors in anorexia nervosa". Pediatrician. 12 (2–3): 134–8. PMID 6400211.
- Eiber, R; et al. (2003). "Self-esteem: a comparison study between eating disorders and social phobia". Encephale. 29 (1): 35–41. PMID 12640325.
- Bulik, C. M.; et al. (1997). "Eating disorders and antecedent anxiety disorders: a controlled study". Acta Psychiatrica Scandinavica. 96 (2): 101–107. doi:10.1111/j.1600-0447.1997.tb09913.x.
- Favaro, A; Tenconi, E; Santonastaso, P (Apr 2008). "The relationship between obstetric complications and temperament in eating disorders: a mediation hypothesis". Psychosom Med. 70 (3): 372–7. doi:10.1097/PSY.0b013e318164604e. PMID 18256341.
- Iidaka, T.; et al. (2006). "Volume of left amygdala subregion predicted temperamental trait of harm avoidance in female young subjects. A voxel-based morphometry study". Brain Res. 1125 (1): 85–93. doi:10.1016/j.brainres.2006.09.015. PMID 17113049.
- Peterson, CB (Jan–Feb 2010). "Personality dimensions in bulimia nervosa, binge eating disorder, and obesity". Compr Psychiatry. 51 (1): 31–6. doi:10.1016/j.comppsych.2009.03.003. PMC . PMID 19932823.
- Gardini, S; Cloninger, CR; Venneri, A (Jun 2009). "Individual differences in personality traits reflect structural variance in specific brain regions". Brain Res Bull. 79 (5): 265–70. doi:10.1016/j.brainresbull.2009.03.005. PMID 19480986.
- Aron, Elaine; Aron, Arthur (1997). "Sensory-Processing Sensitivity and its Relation to Introversion and Emotionality" (PDF). Journal of Personality and Social Psychology. 73 (2): 345–368. doi:10.1037/0022-35188.8.131.525.
- Aron, E.; Aron, A.; Jagiellowicz, J. (2012). "Sensory processing sensitivity: A review in the light of the evolution of biological responsivity" (PDF). Personality and Social Psychology Review. 16 (3): 262–282. doi:10.1177/1088868311434213. Archived (PDF) from the original on May 13, 2015.
- Halmi, KA; et al. (Nov 2000). "Perfectionism in anorexia nervosa: variation by clinical subtype, obsessionality, and pathological eating behavior". Am J Psychiatry. 157 (11): 1799–805. doi:10.1176/appi.ajp.157.11.1799. PMID 11058477.
- Ruggiero, GM.; et al. (Sep 2003). "Stress situation reveals an association between perfectionism and drive for thinness". Int J Eat Disord. 34 (2): 220–6. doi:10.1002/eat.10191. PMID 12898558.
- Hewitt, PL; et al. (2008). "The impact of perfectionistic self-presentation on the cognitive, affective, and physiological experience of a clinical interview". Psychiatry. 71 (2): 93–122. doi:10.1521/psyc.2008.71.2.93. PMID 18573033.
- Frewen, PA; Pain, C; Dozois, DJ; Lanius, RA (Jul 2006). "Alexithymia in PTSD: psychometric and FMRI studies". Ann N Y Acad Sci. 1071: 397–400. doi:10.1196/annals.1364.029. PMID 16891585.
- Guilbaud, O; Corcos, M; Chambry, J; Paterniti, S; Loas, G; Jeammet, P (2000). "[Alexithymia and depression in eating disorders]". Encephale. 26: 1–6. PMID 11192799.
- Smith, GJ; et al. (Aug 1997). "Alexithymia in patients with eating disorders: an investigation using a new projective technique". Percept Mot Skills. 85 (1): 247–56. doi:10.2466/pms.19184.108.40.206. PMID 9293583.
- Peskine, A; Picq, C; Pradat-Diehl, P (Dec 2004). "Cerebral anoxia and disability". Brain Inj. 18 (12): 1243–54. doi:10.1080/02699050410001719899. PMID 15666568.
- Ho, AK; Robbins, AO (Mar 2006). "Barker RAHuntington's disease patients have selective problems with insight". Mov Disord. 21 (3): 385–9. doi:10.1002/mds.20739. PMID 16211608.
- Tchanturia, K; et al. (Sep 2001). "Perceptual illusions in eating disorders: rigid and fluctuating styles". Behav Ther Exp Psychiatry. 32 (3): 107–15. doi:10.1016/s0005-7916(01)00025-8. PMID 11934124.
- Cserjési, R (Jun 2009). "Affect, cognition, awareness and behavior in eating disorders. Comparison between obesity and anorexia nervosa". Orv Hetil. 150 (24): 1135–43. doi:10.1556/OH.2009.28590. PMID 19482720.
- Bechara, A; Damasio, AR; Damasio, H; Anderson, SW (Apr–Jun 1994). "Insensitivity to future consequences following damage to human prefrontal cortex". Cognition. 50 (1–3): 7–15. doi:10.1016/0010-0277(94)90018-3. PMID 8039375.
- Eysenck, SB; Eysenck, HJ (Feb 1977). "The place of impulsiveness in a dimensional system of personality description". Br J Soc Clin. 16 (1): 57–68. doi:10.1111/j.2044-8260.1977.tb01003.x. PMID 843784.
- Welch, SL; Fairburn, CG (Oct 1996). "Impulsivity or comorbidity in bulimia nervosa. A controlled study of deliberate self-harm and alcohol and drug misuse in a community sample". Br J Psychiatry. 169 (4): 451–8. doi:10.1192/bjp.169.4.451. PMID 8894196.
- Corstorphine, E; Waller, G; Lawson, R; Ganis, C (Jan 2007). "Trauma and multi-impulsivity in the eating disorders". Eat Behav. 8 (1): 23–30. doi:10.1016/j.eatbeh.2004.08.009. PMID 17174848.
- Patton, JH; Stanford, MS; Barratt, ES (November 1995). "Factor structure of the Barratt impulsiveness scale". J Clin Psychol. 51: 768–74. doi:10.1002/1097-4679(199511)51:6<768::aid-jclp2270510607>3.0.co;2-1. PMID 8778124.
- Chamberlain, SR; Sahakian, BJ (May 2007). "The neuropsychiatry of impulsivity". Curr Opin Psychiatry. 20 (3): 255–61. doi:10.1097/YCO.0b013e3280ba4989. PMID 17415079.
- Smith, CF (Mar 1998). "Association of dietary restraint and disinhibition with eating behavior, body mass, and hunger". Eat Weight Disord. 3 (1): 7–15. doi:10.1007/bf03354907. PMID 11234257.
- Bryant, EJ; King, NA; Blundell, JE (Sep 2008). "Disinhibition: its effects on appetite and weight regulation". Obes Rev. 9 (5): 409–19. doi:10.1111/j.1467-789X.2007.00426.x. PMID 18179615.
- Grekin, ER; Sher, KJ; Wood, PK (December 2006). "Personality and substance dependence symptoms: modeling substance-specific traits". Psychol Addict Behav. 20: 415–24. doi:10.1037/0893-164X.20.4.415. PMID 17176176.
- Young, SE; Stallings, MC; Corley, RP; Krauter, KS; Hewitt, JK (October 2000). "Genetic and environmental influences on behavioral disinhibition". Am. J. Med. Genet. 96: 684–95. doi:10.1002/1096-8628(20001009)96:5<684::aid-ajmg16>3.0.co;2-g. PMID 11054778.
- Young, SE; et al. (Feb 2009). "Behavioral disinhibition: liability for externalizing spectrum disorders and its genetic and environmental relation to response inhibition across adolescence". J Abnorm Psychol. 118 (1): 117–30. doi:10.1037/a0014657. PMC . PMID 19222319.
- Emond, V; Joyal, C; Poissant, H (Apr 2009). "Structural and functional neuroanatomy of attention-deficit hyperactivity disorder (ADHD)". Encephale. 35 (2): 107–14. doi:10.1016/j.encep.2008.01.005. PMID 19393378.
- Spiegel, DR.; Qureshi, N. "The successful treatment of disinhibition due to a possible case of non-human immunodeficiency virus neurosyphilis: a proposed pathophysiological explanation of the symptoms and treatment". General Hospital Psychiatry. 32: 221–224. doi:10.1016/j.genhosppsych.2009.01.002.
- Aarsland, D; Litvan, I; Larsen, JP (2001). "Neuropsychiatric symptoms of patients with progressive supranuclear palsy and Parkinson's disease". J Neuropsychiatry Clin Neurosci. 13 (1): 42–9. doi:10.1176/appi.neuropsych.13.1.42. PMID 11207328.
- Eysenck, H.J, Eysenck, S.B.G (1977). Psychoticism as a Dimension of Personality. London: Hodder and Stoughton. ISBN 0-340-20919-4.
- Lester, David (1989). "A NEUROTRANSMITTER BASIS FOR EYSENCK'S THEORY OF PERSONALITY". Psychological Reports. 64 (1): 189–190. doi:10.2466/pr0.19220.127.116.11. ISSN 0033-2941. PMID 2564688.
- Zubieta, JK (1995). "Obsessionality in eating-disorder patients: relationship to clinical presentation and two-year outcome". J Psychiatr Res. 29 (4): 333–42. doi:10.1016/0022-3956(95)00020-6. PMID 8847659.
- Salkovskis, PM; Forrester, E; Richards, C (1998). "Cognitive-behavioural approach to understanding obsessional thinking". Br J Psychiatry Suppl (35): 53–63. PMID 9829027.
- Corcoran, KM; Woody, SR (Jan 2008). "Appraisals of obsessional thoughts in normal samples". Behav Res Ther. 46 (1): 71–83. doi:10.1016/j.brat.2007.10.007. PMID 18093572.