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PSY100 – Personality Approaches to the Scientific Study of Personality Describing and Measuring Individual Differences Validating Individual Difference Measures Important Consequences of Individual Differences Causes of Individual Differences.

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PSY100 – Personality

  • Approaches to the Scientific Study of Personality
  • Describing and Measuring Individual Differences
  • Validating Individual Difference Measures
  • Important Consequences of Individual Differences
  • Causes of Individual Differences

How does Personality Psychology differ from Other Disciplines in Psychology?

  • Cognitive psychology: The science of basic cognitive processes
  • Neuropsychology: The science of the connection between the brain and the mind
  • Social psychology: The science of social influences on psychological processes
  • Developmental psychology: The science of changes in psychological processes over the life span.

All these disciplines implicitly assume that all people are the same.

  • Personality psychology makes a different assumption: People are different from one another in important ways.
  • Cognitive “Why do some people have better memories than others?”
  • Social “Why do people respond differently to rejection by others?”
  • Developmental “Why are some children more afraid of strangers than others?”

Two Approaches to Personality:

Idiographic versus Nomothetic Approach

The idiographic (person-centered) approach:

A focus on one individual at a time, and it tries to understand this individuals’ actions from the individuals’ characteristics.

The nomothetic (variable-centered) approach

A focus on the relation between a certain outcome such as academic achievement (getting an A in this class) to a variable like organized-disorganized.


Idiographic Nomothetic

Traditional ModernGrand Theories Small TheoriesOne individual at a time Large samplesQualitative QuantitativeFreud Eysenck Idiographic question: Why did Mariah Carey have a nervous breakdown?

Nomothetic question: Are young stars in the music industry more likely to suffer a nervous breakdown than normal people?


Freud & Rogers – It is impossible to test scientific theories with case studies.

  • Skinner – Behaviorism assumed that all people are born equal and that individual differences are a mere consequence of different learning experiences. Nobody believes this anymore.
  • Eysenck – An influential early proponent of the nomothetic approach. Although unnecessarily confrontational, his work continues to influence modern personality research.

Important Notice

  • As noted in the textbook, “in recent decades the study of personality has shifted toward narrower research programs that examine specific aspects of personality”
  • In other words, most contemporary personality research takes the nomothetic approach.
  • Consistent with this modern trend, my second year course “PSY230 – Introduction to Personality” focuses exclusively on the modern, nomothetic approach to personality psychology.


If you want to learn more about psychodynamic theories (Freud, Adler, Jung), DO NOT take PSY230

However, I hope to convince you in the rest of today’s lecture that the nomothetic approach examines interesting questions and provides answers that are relevant to the understanding of yourself and others.


The Scientific (Nomothetic) Study of Personality and Individual Differences

  • Three Goals of Personality Psychology
  • Classification: How do people differ?
  • Causes: Why do individuals differ from each other?
  • Consequences: What are the effects of individual differences?


  • How consistent are people in their behaviors? When somebody is friendly to us, how likely is it that this person is also friendly to others.
  • Why are some people friendlier than others? Nature vs. nurture – How much is personality due to genetic differences? How much influence do parents have on their children’s personality?
  • What are the consequences of personality?Does personality predict important life-outcomes such as longevity, happiness, and income?

The Scientific Study of Individual Differences

  • The nomothetic approach to personality research relies heavily on correlations (textbook pp. 54-56).
  • Correlations provide information about the relation between variability in two variables.


  • Stability: Will individual differences in today’s friendliness be the same in the future?
  • Consistency: Are individual differences in friendliness in one situation the same in a different situation?
  • Cause: Do genetic differences predict individual differences in friendliness?
  • Consequences: Do individual differences in friendliness predict individual differences in happiness?

Describing Individual Differences

  • Everyday language provides thousands of words to describe individuals (honest, caring, ambitious, orderly, shy, modest, self-confident,…)
  • Correlations (and more advanced statistics) show that individual differences in some of these traits (characteristics) are related (e..g, shy is negatively related to confident).
  • As a result, it is possible to describe personality with fewer dimensions.

The Big Five

  • Initially, personality psychologists used different traits to describe personality and there exist hundreds of measures to measure individual differences in these traits.
  • In the past two decades, it was discovered that these measures are related to each other and can be reduced to five major traits that differentiate one individual from another.
  • The Big Five provide a comprehensive first impression of an individual. They do not capture all aspects of individual differences.

The Atlas Analogy

  • I like to compare the Big Five to continents.
  • Continents capture important differences between regions of the word (Europe is different from Asia).
  • However, there still exists important differences between countries in each continent (Germany is different from Italy).

The Big Five

  • Neuroticism – A disposition to experience more negative feelings and low self-esteem.
  • Extraversion – A disposition to be outgoing, risk-taking, and cheerful.
  • Openness – A disposition to be curious and interested in novel and unconventional things.
  • Agreeableness – A disposition to be caring and modest
  • Conscientiousness – A disposition to be organized, ambitious, and dependable.

Measuring Personality Traits

  • Self-report: The easiest and most widely used method (e.g., “I am self-confident”). Assumes that people are honest and know themselves.
  • Informant reports: asking acquaintances (e.g., Joe is self-confident); more difficult to obtain; assumes that others’ know the person well.
  • Observing behavior: e.g., research assistants rate personality based on videotapes of behavior; time-consuming

Experience sampling: ask participants to keep a diary or momentary records of their thoughts, feelings, and behaviors. Time-consuming, requires high motivation and honesty of participants.

  • Each methods has its advantages and drawbacks.
  • The best way of measuring personality would be to use multiple methods. For example, we are currently conducting a study of married couples in which we assess personality with self-reports, informant reports, and experience sampling.

I tend to be relaxed and handle stress well. I tend to worry a lot.I tend to be quiet. I tend to be outgoing and sociable.I tend to be original and come up with ideas. I tend to like to reflect and to play with ideas. I tend to be considerate and kind to almost everyone. I tend to be rude to others. I tend to do a thorough job. I tend to do things efficiently.

1 2 3 4 5 6 7Strongly disagree strongly agree


Scoring of Your Personality Test

N 1+2 8.60 3.00

E 3+4 9.01 3.00

O 5+6 9.73 2.35

A 7+8 11.39 2.00

C 9+10 10.53 2.09


Stability of Personality

  • Relative differences in personality are quite stable over time.
  • Stability increases over the life-span. It is not fixed at 20.
  • Personality changes with age: - Neuroticism, Extraversion, Openness decrease.- Agreeableness, Conscientiousness increase.

Consequences of Personality

  • Personality and Health
  • Personality and Longevity
  • Personality and Happiness
  • Personality and Marital Satisfaction (Divorce)
  • Personality and Job Performance (Income)

Personality and Health

  • Stress is related to illness – Suppression of the immune system.
  • Neuroticism is related to stress-reactivity.
  • We would expect neuroticism to be related to health.
  • However, neuroticism is more related to subjective perception of symptoms (hypochondria) than to objective health.

Personality and Longevity

  • It is difficult to study the relation between personality and longevity.
  • The Terman-study assessed personality of gifted children in the 1920s and 1930s. Now researchers can examine which children are still alive.
  • Conscientiousness is the best predictor of longevity.
  • The processes underlying this relationship are still unclear.

Personality and Happiness

  • Extraversion is a disposition to experience more positive affect (pleasant feelings).
  • Neuroticism is a disposition to experience more negative affect (unpleasant feelings).
  • Extraversion and Neuroticism are the most important personality predictors of life-satisfaction.

Personality and Marital Satisfaction

  • Research on personality and marital satisfaction has a long history (since 1930s).
  • Most studies show a negative effect of neuroticism on marital satisfaction and a positive effect on divorce.
  • Another interesting finding is that people do not marry on the basis of personality: Spouses’ personality scores are uncorrelated.

Personality and Job Performance

  • It is plausible that some personality traits help people in certain jobs: - extraversion & service jobs - optimism & sales jobs
  • In addition, conscientiousness is a good predictor of job performance in many different jobs (work ethic)
  • Conscientiousness becomes a stronger predictor of job performance with higher autonomy.

Causes of Personality

  • The relative contribution of genetic/biological factors versus environmental/cultural factors has been a major controversy.
  • After the first child parents believe in environmental factors.
  • After the second child parents believe in genetic factors.
  • What is the evidence?

Twin Studies

  • Before DNA testing (before the 1990s), researchers had to rely on indirect evidence to examine the influence of nature (genes) and nurture (environment).
  • Twin studies capitalized on the difference between monozygotic twins (MZ) and dizygotic twins (DZ).
  • MZ twins are genetically identical.
  • DZ twins share on average 50% of their genes, just as much as other siblings.

Genetic Contribution to Personality

  • To examine a genetic contribution, we can compare the similarity of MZ twins to the similarity of DZ twins.
  • (Given certain assumptions), if MZ twins are more similar to each other than DZ twins, then genes must influence the trait.
  • For example, the height of MZ twins correlates very highly (r = .90), whereas the height of DZ twins is correlated less highly (r = .45).
  • Height is genetically determined.

Numerous studies have demonstrated greater similarity (higher correlations) for MZ twins than for DZ twins for personality traits including the Big Five.

  • Today nobody doubts that genetic factors contribute to personality.
  • Twin studies also lead to the conclusion that growing up in the same household has no influence on personality.
  • This finding is the topic of a heated debate as it is hard to believe that parents have no influence on the personality of their children.

Do Genes Determine Personality?

  • Genes cannot directly influence experiences and behavior.
  • Genes influence biological processes, which in turn influence experiences and behavior.
  • Understanding these processes can help people to change their personality.

Neuroticism has been linked to a gene that influences the reuptake of serotonin in the brain.

  • Drugs like Prozac (SSRIs) change the biological reuptake mechanism.
  • Studies show that drugs like Prozac change personality scores on a Neuroticism scale.
  • SSRIs also have several side-effects. They are used only when people suffer from abnormal levels of depression and anxiety.
  • What should we do when it becomes possible to change personality at will?

Cultural influences on personality

  • Cross-cultural studies show variation in personality traits across cultures. For example, HK Chinese score lower on Extraversion and Openness.
  • Acculturation studies show that personality changes. HK Chinese who migrated to Canada have higher extraversion and openness scores.
  • In North America, Extraversion and Neuroticism scores have increased over the past decades.


  • Personality psychology examines individual differences.
  • It relies more on correlations than on experimental studies.
  • It examines the major traits that differentiate people.
  • It examines the consequences of individual differences for real-world outcomes.
  • It examines the causes of individual differences.