Development of a short osteoporosis quality of life questionnaire by equating items from two existing instruments

This study aimed to develop a short Osteoporosis-Specific Quality of Life Questionnaire based on the assemblage (equating) of the items of two existing questionnaires (OQLQ and QUALEFFO). For this purpose, each questionnaire was administered by random assignment to a different group of female patients (OQLQ, n = 172; QUALEFFO, n = 166) with vertebral fractures due to osteoporosis. A common anchor test (SF-36) was also given to both groups. Seven different sets of OQLQ-QUALEFFO common items were defined by inspecting their own correlation with the scores of the eight dimensions of the SF-36. Within each set, equating consisted in connecting the OQLQ and QUALEFFO through their link with the SF-36. Equating was carried out through the Rasch mathematical model. Quantitative (item statistics) and qualitative reductions (expert opinion) of the equated sets resulted in a 16-item questionnaire. Although the new instrument requires further empirical validation, it provides a promising alternative to currently existing longer questionnaires for use in clinical practice.