Financial incentives influence ImPACT validity indices but not cognitive composite scores.

INTRODUCTION: Interpreting change in cognitive performance across baseline and post-concussion evaluations is complicated by poor understanding of how incentives, such as return-to-play, may impact performance. This study examines the influence of an anticipated financial incentive on two sets of outcomes from the ImPACT computerized battery: (a) cognitive composites, meant to serve as measures of cognitive function, and (b) validity indices, proposed as indicators of invalid performance.

METHOD: 81 uninjured college students, randomized into two groups, completed a concussion assessment battery including ImPACT. The control group received standard administration instructions. The incentive group was told they would receive $20 if their scores ranked in the top third of students who completed testing. Test examiners were blinded to condition, and participants were debriefed upon study completion.

RESULTS: Given the non-normal distribution of the ImPACT cognitive composites and validity indices, non-parametric statistics were used to compare performance between incentive and control groups. Results of Mann-Whitney U tests revealed no significant differences between groups on the ImPACT cognitive composites (all p > .05, r = .04 to .19). In contrast, compared with the control group, the incentive group performed significantly better on all five validity indices: Impulse Control Composite (p = .036, r = .23); Xs and Os Total Incorrect (p = .035, r = .23); Word Memory Learning Percent Correct (p = .036, r = .23); Design Memory Learning Percent Correct (p = .018, r = .26); and Three Letters Total Letters Correct (p = .027, r = .25).

CONCLUSIONS: Expectation of financial incentive did not influence performance on the four cognitive composites-the ImPACT's standard metrics of cognitive function. However, the incentive group, relative to controls, exhibited better performance on each of the five validity indices. These results suggest that ImPACT validity indices are more sensitive to incentive-related changes in effort than the ImPACT cognitive composites, providing support for the validity indicator indices as measures of effort toward testing.