Hartshorne · Psychological science 2015 · Cross-sectional observational study and normative dataset analysis · n=48,537

When does cognitive functioning peak? The asynchronous rise and fall of different cognitive abilities across the life span.

Cited 812 times in the scientific literature.

Level 4 - case-series / case-control

Cross-sectional observational study and normative dataset analysis (graded by design analogy).

PubMed 25770099 · doi:10.1177/0956797614567339 · record verified 2026-08-26

What was done

Analyzed lifespan trajectories of cognitive functioning by combining data from 48,537 online participants with normative data from standardized IQ and memory tests.

What was found

The abstract reports no specific numerical effect sizes or test scores. It identified marked heterogeneity in when cognitive abilities peak: some abilities peak and start declining around high school graduation, others plateau in early adulthood and decline in the 30s, and others peak in the 40s or later.

Why it matters

Demonstrates that human cognitive faculties do not peak at a single uniform age, supporting a model where distinct cognitive domains mature and decline along asynchronous timelines.

Limits

The abstract provides no exact statistics, effect sizes, or specific task names. Relying on cross-sectional online data and normative test cohorts limits causal inference regarding individual longitudinal decline due to potential cohort and selection effects.

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