Studies were included in the meta-analyses if they:
- provided at least one correlation coefficient (or convertible effect size) and the associated sample size,
- presented a non-select sample of all relevant correlations/effect sizes (i.e., not just significant correlations/effect sizes and/or partial correlations), and
- used psychological variable level measurement (as opposed to task indicators for cognitive ability or single behavioral indicators for personality).
Certain variables, types of measurement, and information sources were outside the scope of this study:
- other-ratings and/or observer ratings of personality,
- state measures of personality or mood,
- attitudes,
- vocational and leisure interests,
- subjective ratings of cognitive ability (e.g., self-estimates of ability),
- emotional intelligence,
- metacognition,
- attributional complexity,
- school grades (e.g., GPA),
- A/O Level Examinations (i.e., high school graduation proficiency examinations in the UK),
- performance or assessment center rating, and
- pathological samples
- Ipsative personality measures were also excluded since there is some evidence indicating that such measures are more cognitively demanding (and therefore more highly correlated with cognitive ability) than normative measures of personality (Vasilopoulus, Cucina, Dyomina, Morewtiz, & Reilly, 2006). Normative measures of personality require respondents to make a single decision: indicating how much they agree or disagree with an item. Forced choice measures require multiple decisions: indicating how much they agree or disagree with an item and also ranking the item relative to the rest of the alternatives. Consequently, ipsative measurement of personality traits may artificially inflate correlations with cognitive ability constructs. As a result, ipsative personality measures may display artifactually stronger relations with cognitive ability than single-stimulus measures (Vasilopoulos et al., 2006).
- Finally, samples with participants younger than 12 years old were excluded in an attempt to report only on relatively stable (Briley & Tucker-Drob, 2013) and normative trait variation. This age also coincides with the United Nations convention on the typical minimum age at which children can start working in most countries (United Nations International Law Convention No. 138, 1973).
- Psychomotor ability and auditory processing constructs were only convenience-sampled (i.e., only coded when the study also reported relations for other ability constructs) since it was decided partway through the project that such constructs represent a broad cognitive ability domain with a vast literature of its own.