Reliability and Construct Validity of Self-Report Questionnaires for Patients With Pelvic Girdle Pain

Abstract

There is little evidence for the measurement properties of instruments commonly used for women with pelvic girdle pain. The aim of this study was to examine the internal consistency, test-retest reliability, and construct validity of instruments used for women with pelvic girdle pain. This was a cross-sectional methodology study, including test-retest reliability assessment. Women with pelvic girdle pain in pregnancy and after delivery participated in a postal survey that included the Pelvic Girdle Questionnaire (PGQ), Oswestry Disability Index (ODI), Disability Rating Index (DRI), Fear-Avoidance Beliefs Questionnaire (FABQ), Pain Catastrophizing Scale (PCS), and 8-item version of the Medical Study 36-Item Short-Form Health Survey questionnaire (SF-36). Test-retest reliability was assessed with a random subsample 1 week later. Internal consistency was assessed with the Cronbach alpha, and test-retest reliability was assessed with the intraclass correlation coefficient (ICC) and minimal detectable change (MDC). Construct validity based on hypotheses was assessed by correlation analysis. Discriminant validity was assessed with the area under the receiver operating characteristic curve. All participants responded to the main (N=87) and test-retest (n=42) surveys. Cronbach alpha values ranged from .88 to .94, and ICCs ranged from .78 to .94. The MDC at the individual level constituted about 7% to 14% of total scores for the 8-item version of the SF-36, ODI, and PGQ activity subscale; about 18% to 22% for the DRI, PGQ symptom subscale, and PCS; and about 25% for the FABQ. Hypotheses were mostly confirmed by correlations between the instruments. The PGQ was the only instrument that significantly discriminated participants who were pregnant from participants who were not pregnant as well as pain locations. A comparison of responsiveness to change of the various instruments used in this study was not undertaken, but will be carried out in a future study. Self-report instruments for assessing health showed good internal consistency, test-retest reliability, and construct validity for women with pelvic girdle pain. The PGQ was the only instrument with satisfactory discriminant validity, thus, it is recommended for evaluating symptoms and disability in patients with pelvic girdle pain.