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.

Notes

Jo Nijs, PhD, MSc, MT, PT;Department of Human Physiology, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel (VUB), Belgium. [email protected]

Benedicte Cloostermans, PT; Division of Occupational and Physical Therapy-Department of Health Sciences-Hogeschool Antwerpen, Belgium.

Neil McGregor, MDSc, PhD; Collaborative Pain Research Unit-Department of Biological Sciences-Faculty of Science-University of Newcastle, Callaghan, New South Wales, Australia.

Peter Vaes, PhD, PT; Department of Physical Therapy, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel (VUB), Belgium.

Kenny DeMeirleir, MD, PhD. Department of Rehabilitation Science and Physical Therapy-Faculty of Physical Education and Physical Therapy-Vrije Universiteit Brussel (VUB), Belgium.