Previous research has consistently shown an association between depression and disability in the elderly but little is known about the mechanisms linking the two. Recent longitudinal population studies have shown considerable inconsistency in the criteria used to establish causality and terms such as mediation and effect modification have been frequently applied incorrectly in terms of the inferences drawn. We underline the necessity to adopt more stringent theoretical criteria for the establishment of intermediary effects in the relationship between depression and disability to better identify cross-validated potential intervention points for reducing the risk of disablement and depression.