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Data sources

Inferences about personality can be made from a number of different data sources: self-report (S-data), informant-report (I-data), life-outcome (L-data), test (T-data)


Self-report data

Most frequently used type of data when making inference about personality --> clinical interviews, self-report questionnaires

Strengths: individuals have access to information about themselves that is inaccessible to anyone else

Limitations: respondents must be willing and able to answer honestly and consistently [unsystematic error --> carelessness and indifference, systematic error --> acquiescence (tendency to simply agree to items), impression management (faking/lying esp with undesirable traits), self-deception (social desirability)]


Informant-report data

Another way to learn about an individual's personality is to father the impressions or evaluations of knowledgeable informants

Strengths: some traits crucially depend upon the report of others ie popularity, for those with limited ability to self-report

Limitations: view of personality for the outside, restricted to a limited number of situations, informant bias


Life outcomes data

Biographical data obtained from archival records that are available to public scrutiny - the "residue" of personality

Strengths: information in archival records is typically accurate and not prone to the potential biases of S-data or I-data.

Limitations: life outcomes are determined by a multitude of different factors and may reveal very little about personality


Test data

Participants are either placed or found in a "testing situation" and their behaviour is directly observed.

Strengths: gathering own information, allows for precise objective and quantifiable measurement of variables

Limitations: uncertain interpretation


Constructing self-report scales

1. Identifying potential questionnaire items (rational approach, empirical approach, theoretical approach)
2. Factor analysis of questionnaire items (correlation matrix and factor loadings)
3. Evaluation of questionnaires --> reliability (test-retest, internal consistency, inter-rater) & validity (face, criterion-related, construct)


Rational approach

Common sense based around the lexical hypothesis: that all important personality traits must have been encoded within the natural language.
4.5% of total English vocabulary trait terms
Four categories --> real traits of personality; present activity, temporary states of mind and mood; character evaluations; behaviour, physical qualities, talents


Empirical approach

A largely a theoretical approach which employs criterion groups extreme on the trait or characteristic of interest (clinical and normal) --> criterion-keying


Theoretical approach

Uses a given theoretical perspective to determine content for the initial item pool


Trait data for nomothetic research

Personality questionnaires (self-report, informant-report) are typically used. T-data with children & L-data as supplementary.

Often in nomothetic research, questionnaire measures of S or I-data used to predict: L-data (eg divorce) & T-data (eg physiological reactivity).


Evaluating self-report scales

Reliability: test-retest, internal consistency, inter-rater

Validity: face validity, criterion- related, construct



Precision in measurement.

Precision is determined by the consistency of scores obtained by the same person on repeated measures.


Test-retest reliability

The correlation between scores obtained by the same persons on an identical test administered on two separate occasions (usually 1mth apart).

If correlation is low, test might be measuring a transient state rather than a stable trait.

When interval between tests is greater than 6mths, correlation coefficient is typically referred to as a stability coefficient (rather than a reliability coefficient).


Internal consistency

Split-half reliability (involves correlating one half of the test with the other)
Cronbach's alpha (the average of all possible split-halves --> both halves of the test should rank people in a similar way, if not the consistency attributed to error in content sampling)


Inter-rater reliability

The degree of agreement/consistency between 2+ raters/scorers


Criterion-related validity

Predictive validity

Requires some relationship be established between test scores and some criterion external to that test

Eg scores on a test of sociability should predict the number of conversations a person initiates.


Construct validity

Refers to whether or not a test measures the unobserved theoretical construct it purports to measure

Factorial validity
Convergent & discriminant validity


Convergent & discriminant validity

Convergent validity: can be demonstrated when scores on a test correlate with scores on another test designed to assess the same/similar construct.

Discriminant validity: can be called into question if scores on a test correlate with scores on another test designed to assess a different construct