Development of the Qualeffo–31, an osteoporosis-specific quality-of-life questionnaire |
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Authors: | N M van Schoor D L Knol C A W Glas R W J G Ostelo A Leplège C Cooper O Johnell P Lips |
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Institution: | 1. Institute for Research in Extramural Medicine, VU University Medical Center, Amsterdam, The Netherlands 2. Department of Clinical Epidemiology and Biostatistics, VU University Medical Center, Amsterdam, The Netherlands 3. Department of Educational Measurement and Data Analysis, University of Twente, Enschede, The Netherlands 4. Institut National de la Santé et de la Recherche Médicale (INSERM), Unité 292, H?pital de Bicêtre, Le Kremlin–Bicêtre, France 5. MRC Epidemiology Resource Centre, University of Southampton, Southampton, UK 6. Department of Orthopaedics, Malm? General Hospital, Malm?, Sweden 7. Department of Endocrinology, VU University Medical Center, P.O. Box 7057, 1007, Amsterdam, The Netherlands
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Abstract: | 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 ≥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. |
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Keywords: | Item response theory Quality of life Qualeffo– 31 Qualeffo– 41 Vertebral fracture |
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