How strong is the evidence for mediational hypotheses of age-related memory loss? Commentary

Background: Luszcz and Bryan review research supporting th ree theories of age-related memory loss: the speed hypothesis, the executive function hypot hesis, and the common cause hypothesis, Objective: The aim of this commenta ry is to extend that review by encouraging consideration of the strength (o r lack thereof) of the empirical evidence supporting theories of age-relate d memory loss, Methods: Arguments are presented that call into the question the strength of the evidence that derives from cross-sectional analysis of individual difference sources of variance. Results: Supporting evidence fo r mediational hypotheses of cognitive aging (1) derives from potentially am biguous statistical techniques; (2) is based on untested assumptions about the between and within person sources of variance; (3) is not supported by longitudinal studies, and (4) relies heavily on arguments of parsimony. Con clusions: Existing evidence is not strong enough to grant any particular th eory presumptive status, We concur with Luszcz and Bryan that supplementing the now popular individual differences research designs with alternative a pproaches would advance theory development and testing. Copyright (C) 1999 S. Karger AG, Basel.