Standard Neuropsychological Tests of Cognition
The standard way to measure cognition in clinical practice and intervention trials is with standardized neuropsychological tests. The tradition in clinical neuropsychological assessment has been to perform a detailed assessment aimed at examining a variety of cognitive domains to document level of abilities or changes in abilities (Heaton, Grant, & Matthews, 1991; Reitan & Wolfson, 1993). These measures are also sometimes used as mediating variables to describe how changes in a targeted outcome measure (e.g., some aspect of functional performance) observed after the implementation of an intervention are mediated by changes in cognition (see Chapter 13).
There is a wide variety of neuropsychological measures available and they are generally linked to a specific cognitive domain/ability (e.g., working memory, attention). It is beyond the scope of this chapter to review the comprehensive and somewhat unyielding list of available measures. Although these specific cognitive domains can be defined and measured with neuropsychological tests, there are two important points to consider. First, the neuropsychological tests that are targeted at different domains of functioning are often highly intercorrelated (Dickinson, Ramsey, & Gold, 2007), and the best fitting factor structure is a single, global factor (Keefe, Bilder, et al., 2006). On the other hand, scores on tests measuring similar cognitive domains, such as elements of intelligence, are often somewhat discrepant from each other in healthy people (Zakzanis & Jeffay, 2011), indicating that variability in performance across domains is not abnormal.
Further, there is often disagreement among researchers about which measures are optimal for each domain and population of interest (e.g., minority vs. nonminority). In this regard, the National Institutes of Health (NIH) Toolbox includes a set of brief measures that can be used to assess cognitive, emotional, motor, and sensory functions in individuals aged 3 to 85. The intent of the development of the NIH Toolbox was to harmonize measurement of functions across diverse study designs and settings (www.nihtoolbox.org).