Retest effects in serial cognitive testing can mask a year or more of genuine age-related decline

A secondary analysis of trial data from 977 community-dwelling older adults in the United States examined how repeated neuropsychological testing affects apparent cognitive change over time Primary Study. Retest effects — improvement in scores attributable simply to prior exposure to the same tests, rather than genuine change — were large enough to offset roughly a year of expected age-related decline across global cognition, executive function and memory.

This is a methodological rather than an intervention finding, derived from a well-characterised, multi-site US trial population. The precise magnitude of the effect may not transfer exactly to other test batteries or populations, but the underlying phenomenon — that repeat testing itself inflates apparent stability or improvement — is a general feature of serial neuropsychological assessment, not one specific to this trial.

The implication is a methodological caution for any service using serial cognitive testing to track decline or treatment response: an apparent year of stability or improvement on repeat testing could reflect the retest effect rather than a genuine clinical signal, and interpretation of serial scores should account for this.