Construct validity and internal consistency of the chronic fatigue syndrome activities and participation questionnaire (CFS-APQ)

Abstract

Identifying patients' activity limitations is crucial for teaching Chronic Fatigue Syndrome (CFS) patients to effectively manage their activity level. Therefore, a questionnaire to assess activity limitations/participation restrictions in CFS patients was recently constructed. In this study, the internal consistency, the discriminant validity, and the convergent validity of this measure, named the CFS-Activities and Participation Questionnaire (CFS-APQ), were investigated. Convergent and discriminant validity are considered two fundamental aspects of construct validity. An envelope containing the CFS-APQ and the Medical Outcomes Short Form 36 Health Status Survey (SF-36) was sent to 149 CFS patients. Eighty-eight out of 149 CFS patients (59.1%) filled in and returned the questionnaires. Cronbach's Alpha reliability coefficients were >0.87. The CFS-APQ total scores correlated statistically significant with six out eight SF-36 subscales (bodily functioning, physical role functioning, bodily pain, general health perception, vitality and social functioning), with Spearman Rank correlation coefficients ranging from −0.34 to −0.78. The highest correlation coefficients were obtained between the CFS-APQ total scores and the subscales ‘physical functioning’ and ‘social functioning’, no significant correlations were observed with the SF-36 subscales emotional role functioning and mental health. In conclusion, the items of the Dutch version of the CFS-APQ have been found to have good internal consistency, and these results substantiate both the convergent and the discriminant validity of the scores obtained with this questionnaire.