Psychometric properties of 12-item World Health Organization disability assessment schedule 2.0 (WHODAS 2.0) amongst people with chronic musculoskeletal pain

Abstract

Aim of this thesis was to explore the floor and ceiling effect, differential item functioning (DIF), minimal clinically important difference (MCID) and minimal detectable change (MDC) of 12-item World Health Organization Disability Assessment Schedule (WHODAS) 2.0 amongst people with chronic musculoskeletal pain. Of the cross-sectional data of 1 988 patients seen at Physical and Rehabilitation Medicine (PRM) clinic, 65 % were women. The mean age was 48 years, and the average score of 12–item WHODAS 2.0 was 13/48 points. Of the participants, 88% had a primary diagnosis of ‘Diseases of the musculoskeletal system and connective tissue'. Of those, 39% had a diagnosis of ‘Dorsalgia’. Floor and ceiling effects were calculated as relative frequencies of the lowest or the highest scores for each item. The DIF was tested using logistic regression analysis and the Chi2 test and interpreted graphically based on item characteristic curves. The MDC and MCID were calculated based on the variance of the scores. A systematic review explored the evidence of the psychometric properties of 12-item WHODAS 2.0 among general population and people with non-acute physical causes of disability. The 12-item WHODAS 2.0 demonstrated high, almost nine points MDC. As the MDC exceeded the level of MCID, nine points were considered to be the amount of change perceived by a respondent as clinically significant. A significant floor effect (>15%) was seen in all 12 items. A significant uniform gender-related DIF was detected in 7 of 12 items. In conclusion, due to the floor effect, the 12-item WHODAS may have limitations in the lower end of the scale amongst people with milder disability. Seven items functioned differently between men and women and almost nine points MDC might complicate the use of WHODAS 2.0 total score. It appears that it is a multidimensional scale, and its total score may represent different combinations of several contributing factors. Therefore, all these findings should be taken into consideration while making the work ability or rehabilitation evaluations or interpreting the results based on the single total score instead of item scores in patients with chronic musculoskeletal pain.