Computer adaptive testing (CAT) is mentioned as a promising gateway for solving the methodological restrictions that are present in today's outcome instruments. One of the challenges facing researchers today is incorporating tests that clearly differentiate between the concept of disability and functional limitations. An emphasis on behavior in disability assessment contrasts it with the concept of functional limitation, where the focus is on assessing the individual's capacity to do specific tasks or activities. The author uses the Late-Life Function and Disability Instrument (Late-Life FDI) to show the type of work that needs to be done in this area. Items that assess disability include questions that pertain to a wide variety of life roles (beyond the traditional focus on Activities of Daily Living (ADLs) and Instrumental Activities of Daily Living (IADLs) and describe the individual's regularity of participating in different behaviors as well as the capability of performing certain life roles. The function items on the Late-Life FDI assess self-reported difficulty in performing a discrete physical action or task that samples key indicators of functioning.

The second major research challenge is the inability of existing instruments to detect changes in disability in response to physical activity interventions. The problem is in identifying the optimal set of items that are relevant for the entire group under study. Short surveys, such as the Short Form 36 (SF-36) and Late-Life FDI, unfortunately, rely on a fixed set of questions that cannot possibly be the best set for all subjects and purposes. The advantage, however, is that the results can be easily compared.