Use of cognitive interviews in the development of the PLUS-M item bank

Measuring constructs such as mobility with patient-reported outcomes (PROs) can enhance clinical and scientific understanding of how health conditions, like lower limb amputation, impact patients' lives. When developing PRO questionnaires, cognitive interviews (CIs) are used to examine whether survey items are understandable, clear, and meaningful. The aim of this study was to use CIs to inform item development for the Prosthetic Limb Users Survey of Mobility (PLUS-M), a PRO that measures mobility in prosthetic limb users. Thirty-six CIs were conducted with 30 prosthetic limb users. Each participant responded to up to 30 items from the PLUS-M candidate item set. Each item was reviewed by a minimum of five participants who differed in self-reported mobility, literacy, level of amputation, and time since amputation. Items were revised based on participant feedback, and substantially revised items were re-evaluated through additional CIs. Feedback from CIs identified substantial issues in 76 of the total 156 items. These items were subsequently modified or eliminated. Cognitive interviews were an essential qualitative step in the development of the PLUS-M item bank and resulted in better functioning items.