Rasch analysis of the WHOQOL-BREF in post polio syndrome
Ian M. Pomeroy , Alan Tennant, Carolyn A. Young
Department of Neurology, Walton Centre for Neurology & Neurosurgery, L9 7LJ Liverpool, United Kingdom. E-mail: firstname.lastname@example.org
Objective: The World Health Organisation quality of life abbreviated scale (WHOQOL-BREF) was developed as a measure of quality of life across 4 separate health domains; physical health, psychological, social relationships and environment. This study evaluated the validity of the WHOQOL-BREF in post-polio syndrome by testing it for fit against the Rasch model.
Results: The scale was posted to 319 volunteers, 271 (85%) completed the scale with a mean age of 66.7 years (standard deviation 8.15); 64% were female. The social relationships domain fitted the Rasch model (χ2 p = 0.19) but reliability was low (α = 0.69) and there were insufficient items to test the assumption of unidimensionality. Solutions were derived for physical health (p = 0.45, t-test = 1.5%, α = 0.67), psychological (p = 0.19, t-test = 4.9%, α = 0.78) and environment domains (p = 0.48, t-test = 6.0% - lower confidence interval 3.4%, α = 0.80) by accounting for local dependence and to cancel out differential item functioning. An overall measure of quality of life, which combined all 4 domains was validated (p = 0.80, t-test = 4.6%, α = 0.81). A transformation table for this total score is provided.
Conclusion: The 4 domains of the WHOQOL-BREF provide valid measures of quality of life in post-polio syndrome. The summed score was more reliable and better targeted and can be used as an ordinal estimate of quality of life.
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