Objective:
To compare the performance of four reliable change (RC) methods with respect to measuring cognitive change on the Cogstate Computerized Battery (CCB).
Method:
We assessed cognitive change in 57 healthy, urban, well-educated males on the CCB at baseline and 6 months (Median age = 50, 65% university-educated). The study CCB version comprised seven measures covering attention, processing speed, verbal learning, and memory. Raw scores were z-score transformed using age-corrected Cogstate norms (CN) or the sample mean and standard deviation (internal standardization [IS]), and then averaged to create composite z-scores. Composite scores were entered into four RC formulae. RC was defined based on a 90% two-tailed confidence interval. Change scores were compared as continuous (z-scores) and ordinal variables (RC outcomes).
Results:
CCB composite score reliability (rXY = .78-.79) was replicated in an age- and sex-matched Cogstate database sample of similar size. There was good overall agreement between the four RC methods (Bland-Altman Mdiff = .00; 95% limits of agreement with the mean-CN: z = ± .90; IS: z = ± .93), with each model adhering closely to the 10% rate of RC expected by chance alone (largest χ2 = .86, p = .99). Initial norming strategy (CN or IS) did not affect these outcomes.
Conclusions:
Norming strategy and RC method choice did not significantly impact cognitive change predictions on CCB composite scores. A series of example case data are provided to practically demonstrate the steps involved in applying the longitudinal norms generated in this study. Research in more diverse normative samples is warranted.
