Cognitive Composite Scores in WRAP

The composite scores in WRAP were created by averaging several scores from different neuropsychological tests, after first z-transforming each score to put it on a common scale. Such composite scores, which can be either global or domain-specific in nature, can reduce error variance, making it easier to detect subtle longitudinal change (Jonaitis et al., 2019). Starting in Freeze 18, we will make available six composite scores: three global composites inspired by the work of Mike Donohue and colleagues to define a Preclinical Alzheimer's Cognitive Composite that can be used across studies (Donohue et al., 2014), and three domain-specific composites structured after analyses done on WRAP data by Lindsay Clark (Clark et al., 2016). Data in the paper linked above suggests that these composites are more powerful than both the individual raw test scores and the earlier factor scores.

The following table lists the constituent tests in each composite score and, where available, provides a citation in which the composite is described more fully. I have also attached two text files containing the SQL code used to create these composites, as well as a table of coefficients necessary for their calculation.

Prior to Freeze 18, composite scores were not computed in the WRAP database. In Fall 2018, Erin Jonaitis made available to a small number of researchers a dataset containing composite scores that were calculated using Freeze 17 scores for all but Logical Memory. After data lock for Freeze 17, the WRAP team began a quality control project that resulted in many small (one- or two-point changes) to Logical Memory I and II scores. To maximize compatibility with future freezes, the shared Freeze 17 composites incorporated Logical Memory scores captured from the live database in October 2018. This means that researchers wishing to verify composite calculations on Freeze 17 data using the attached code will notice many small discrepancies in all but the Executive Function composite scores.