Comparison of performance-based assessment and real world skill in people with serious mental illness: Ecological validity of the Test of Grocery Shopping Skills

Valid functional measures are essential for clinical and research efforts that address recovery and community functioning in people with serious mental illness. Although there is a great deal of interest in functional assessment, there is limited research supporting how well current evaluation methods provide a true assessment of real world functioning or naturalistic behavior. To address this gap in the literature, the present study examined the performance of individuals with serious mental illness (i.e., diagnosis of schizophrenia-spectrum, bipolar disorder, or other depression/anxiety diagnoses and accompanying functional disability) on the Test of Grocery Shopping Skills (TOGSS), a performance-based naturalistic task. We compared TOGSS performance to two dimensions of real world functioning: directly observed real world grocery shopping and ratings of community functioning. Results indicated that the TOGSS was significantly associated with real life grocery shopping, in terms of both shopping accuracy (r = 0.424) and time (r = 0.491). Further, self-report and observer-rated methods of assessing real world shopping behaviors were significantly correlated (r = 0.455). To our knowledge, this is one of the first studies to directly compare a performance-based naturalistic skill assessment with carefully observed real world performance of that skill in people with serious mental illness. These findings support the feasibility and ecological validity of performance-based naturalistic assessment with the TOGSS.