Although personality and cognitive ability are separate (sets of) constructs, we argue and demonstrate in this article that their effects are difficult to tease apart, because personality affects the performance on cognitive tests and cognitive ability affects the item responses on personality assessments. Cognitive ability is typically measured with tests of items with correct answers; personality is typically measured with rating-scale self-reports. Oftentimes conclusions regarding the personality–ability relationship have as much to do with measurement methods as with the construct similarities and differences. In this article, we review key issues that touch on the relationship between cognitive ability and personality. These include the construct-method distinction, sources of test score variance, the maximal vs. typical performance distinction, and the special role for motivation in low-stakes testing. We review a general response model for cognitive and personality tests that recognizes those sources of test score variance. We then review the approaches for measuring personality through performance (objective personality tests, grit game, coding speed, economic preferences, and confidence), test and survey behavior (survey effort, response time, and item position effects), and real-world behavior (study time, registration latency, behavior residue, and social media). We also discuss ability effects on personality tests, indicated by age and cognitive ability effects, anchoring vignette rating errors, and instructions to ‘fake good’. We conclude with a discussion of the implications for our understanding of personality and ability differences, and suggestions for integrating the fields.
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