An evaluation of analytical approaches for understanding change in cognition in the context of aging and health.

In this article, we discuss the importance of studying the relationship between health and cognitive function, and some of the methods with which this relationship has been studied. We consider the challenges involved, in particular operationalization of the health construct and causal inference in the context of observational data. We contrast the approaches taken, and review the questions addressed: whether health and cognition are associated, whether changes in health are associated with changes in cognition, and the degree of interdependency among their respective trajectories. A variety of approaches for understanding the association between cognition and health in aging individuals have been used. Much of the literature on cognitive change and health has relied on methods that are based at least in part on the reorganization of between-person differences (e.g., cross-lag analysis) rather than relying more fully on analysis of within-person change and joint analysis of individual differences in within-person change in cognition and health. We make the case for focusing on the interdependency between within-person changes in health and cognition and suggest methods that would support this.