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Abstract
Objectives: To investigate the reliability and construct validity of the International Classification of Functioning, Disability and Health [ICF] Comprehensive Core Set for Chronic Widespread Pain [CWP] in order to test its possible use as a measuring tool for functioning.
Methods: Patient participants with CWP were assessed by the ICF Comprehensive Core Set for CWP, the Short Form-36 Health Survey [SF-36] and the Fibromyalgia Impact Questionnaire [FIQ]. The internal construct validity of the “Body Functions” [BF], “Activity” [A], “Participation” [P] and “Environmental Factors” [EF] domains were tested by Rasch analysis; the reliability by internal consistency and the Person Separation Index; and external construct validity by association with the SF-36 and FIQ.
Results: One hundred patients with fibromyalgia syndrome [FMS] were recruited for this study in Ankara, Turkey. Most were literate in Turkish and were able to complete the SF-36 and FIQ unassisted but some were illiterate, so the instruments were read to them by an investigator. In each scale, items showing disordered thresholds were rescored, testlets were created to overcome local dependency problems, and items mismatched to the Rasch model were deleted. Then the internal construct validity of the BF, A, P and EF scales were good, indicating a single underlying construct for each scale. The scales were free of differential item functioning. Reliabilities of the scales were adequate [Cronbach’s alphas 0.78–0.86, Person Separation Index’s 0.68–0.82]. The BF, A and P showed moderate correlations with the SF-36 and FIQ, whereas the EF scale had statistically significant but weak correlation only with SF-36 Social Functioning.
Conclusion: Since the four scales derived from BF, A, P and EF components of the ICF core set for CWP were shown to be reliable and valid through Rasch analysis and classical psychometric methods, these might be used as clinical assessment tools.