Construct overlap in resource theories of memory aging. Commentary.

This article evaluates the conceptual status of working memory, processing speed, executive function and sensory function as mediational constructs to explain memory aging. The main difficulty for these mediational constructs is that they may not be independent. Mediational constructs may overlap with each other or with the dependent variable due to theoretical, substantive or methodological reasons. It is argued that sensory function has an advantage over processing speed, working memory and executive function as a mediational construct because it is non-cognitive. The problem of construct overlap is relevant to both cross-sectional and longitudinal studies. Further research is required to evaluate the relative importance of mediational constructs in theories of memory aging, general intellectual aging and dementia.