Influence of recruitment and participation bias in neuropsychological research among MS patients.

The potential influence of recruitment context in neuropsychological (NP) research is seldom addressed in the literature. Our experience with a previous large-scale study of MS cognitive impairment led us to speculate that referral questions and motivation bias significantly impact conclusions drawn from NP testing. We re-analyzed data from Benedict et al. (2006) and compared the results obtained across three groups of patients: paid research volunteers, clinical patients undergoing evaluation for routine monitoring of cognitive status, and clinical patients referred for diagnostic clarification, determination of disability benefits, and other more complex issues. Research volunteers were significantly younger and less frequently cognitively impaired compared to the clinical groups, greatly affecting prevalence estimates (45.6 to 65.6%). Significant correlations between depression and cognitive impairment were present only among the research volunteers. NP testing significantly predicted vocational outcomes in all groups. These results suggest that greater attention should be paid to the reasons patients agree to participate in NP testing.