Development of the Qualeffo-31, an osteoporosis-specific quality-of-life questionnaire.

INTRODUCTION: Vertebral deformities are a common consequence of osteoporosis and are known to decrease quality of life. The Qualeffo-41 is a quality-of-life questionnaire especially developed for measuring quality of life in patients with vertebral deformities. It consists of 41 questions arranged in five domains: pain, physical function, social function, general health perception, and mental function. The objectives of this study were: (1) to develop a shorter version of the Qualeffo-41 by removing redundant questions; and (2) to investigate the scale characteristics, reliability, and validity of this shorter version. METHODS: The study was performed using data from the Qualeffo validation study and the Multiple Outcomes of Raloxifene Evaluation (MORE) study. The analyses were performed in patients with vertebral deformities (n=579). Factor analysis on polychoric correlations and an item response theory (IRT) model, i.e., the generalized partial credit model (GPCM), were used to create a shorter version of Qualeffo-41. Using GPCM, scoring weights were computed for all items. RESULTS: Three items were removed from the data set because of too many missing values. Factor analysis identified three instead of five domains: (1) pain, (2) physical function, and (3) mental function. Five items had factor loadings <0.4 and were not included in the GPCM. After excluding several items, the domains pain (four items), physical function (18 items), and mental function (nine items) showed a good, reasonable, and excellent fit, respectively. This indicates that the mental function domain and the pain domain are more unidimensional than the physical function domain. All three domains showed a very high correlation (r > or =0.95) with the corresponding domains of the Qualeffo-41. CONCLUSIONS: Qualeffo-31 was developed, consisting of three domains with a reasonable to excellent fit to the GPCM. Although the fit to the GPCM supports the construct validity of the Qualeffo-31, validation in a new study should be performed before using it in practice.