Rasch analysis supported the construct validity of self-report measures of activity and participation derived from patient ratings of the ICF low back pain core set.

OBJECTIVE: To investigate whether measures of activity limitations and participation restrictions with sound internal construct validity could be derived from patient ratings of the International Classification of Functioning, Disability and Health Low Back Pain Core Set (LBP-CS).

STUDY DESIGN AND SETTING: The LBP-CS Self-Report Checklist (LBP-CS-SRC) was developed to permit patients to self-rate their functioning according to an extended set of activity and participation categories from the LBP-CS. Rasch analysis was used to examine the validity of the LBP-CS-SRC with a sample of 308 adults with chronic low back pain attending two tertiary-referral outpatient services in Brisbane, Australia.

RESULTS: The activity limitations and participation restrictions qualifier scales functioned satisfactorily, and the LBP-CS-SRC person response validity was good. After deletion of six misfitting items, the dimensionality results supported using the instrument as distinct measures of activity limitations (17 items) and participation restrictions (10 items). The activity and participation measures both had good person separation reliability, and no component items exhibited meaningful differential item functioning.

CONCLUSION: The results demonstrate that measures of activity and participation with sound internal construct validity can be derived from patient ratings of LBP-CS categories. The LBP-CS-SRC can be used in clinical practice and epidemiologic research to support understanding of patients' perspectives on functioning.