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Psychology study materials
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Psychology: Personality and individual differences (theories, assessment, psychometrics)

Psychology · Work through your exam, one topic at a time.

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Personality and individual differences (theories, assessment, psychometrics)

This domain covers how psychologists describe enduring patterns of behavior and how they measure them. Many items contrast reliability with validity or ask you to interpret a standard score.

Theories

  • Psychodynamic: id (pleasure), ego (reality), superego (morality); defenses include repression, projection, displacement, reaction formation, rationalization. Neo-Freudians emphasized social and cultural factors (Adler, Horney, Jung's archetypes).
  • Humanistic: Rogers (unconditional positive regard, self-concept, congruence), Maslow (need hierarchy).
  • Trait: Allport (cardinal, central, secondary), Eysenck (extraversion, neuroticism, psychoticism), Big Five (openness, conscientiousness, extraversion, agreeableness, neuroticism) as the dominant model, reasonably stable in adulthood with substantial heritability.
  • Social-cognitive: Bandura (reciprocal determinism, self-efficacy), Rotter (locus of control), Mischel (person-situation interaction).

Assessment

  • Projective tests (Rorschach, TAT) rely on ambiguous stimuli and show weaker reliability and incremental validity; objective inventories (MMPI-2/3, NEO-PI-R, 16PF) use standardized scoring, and validity scales catch exaggeration or random responding.
  • Reliability is consistency; validity is accuracy of inference. Reliability limits validity but never guarantees it.

Psychometrics

  • Reliability: test-retest, internal consistency (Cronbach's alpha, split-half), inter-rater. Longer tests are more reliable (Spearman-Brown).
  • Validity: content, criterion or predictive, construct (convergent and discriminant evidence).
  • Standard scores: z = (X minus mean) divided by SD; T = 50 plus 10z; percentiles give the percentage scoring below a raw score.
  • Item analysis: difficulty and discrimination (item-total correlation).

Worked example

A new anxiety scale gives every respondent a score exactly 5 points above their true score. Reasoning: the scale is perfectly consistent, so test-retest reliability is near 1.00, but it is systematically biased, so classification validity is poor. Constant error is a validity problem; random error is a reliability problem.

Traps

Saying a test is valid because it is reliable; reading a percentile as percent correct; treating heritability as a fixed property of one individual rather than a population statistic; calling the MMPI projective.