Assessing the responsiveness of a functional status measure: the Sickness Impact Profile versus the SIP68

In this study, the Sickness Impact Profile (SIP) and the SIP68 are studied for their ability to detect changes in health-related behavioral status. Methodological approaches toward responsiveness are invented and discussed. Next, literature findings on the responsiveness of the SIP are presented and judged for their validity. The SIP appeared to be able to demonstrate changes in the expected direction and in accordance with changes detected by other instruments. Using data from seven different longitudinal projects in populations with different diagnoses, the responsiveness of both the SIP136 and the SIP68 are subsequently studied and compared. In all populations, changes in functional status were indicated by both instruments. In terms of effect sizes, the SIP136 and the SIP68 do not differ significantly in their responsiveness. Moreover, changes detected by both SIPs appear to be valid representations of changes in health-related functional status.