Evidence of Validity for the Hip Outcome Score

PURPOSE: The purpose of this study was to offer evidence of validity for the Hip Outcome Score (HOS) based on internal structure, test content, and relation to other variables. METHODS: The study population consisted of 507 subjects with a labral tear. Internal structure was evaluated by use of factor analysis and coefficient alpha. Test content was evaluated by use of item response theory. Pearson correlation coefficients were used to assess relations between the Short Form 36 and the HOS. RESULTS: The mean subject age was 38 years (range, 13 to 66 years), with 232 male and 273 female subjects. Of the subjects, 263 (52%) underwent arthroscopic surgery. Factor analysis found that 17 of 19 items on the activities-of-daily-living (ADL) subscale loaded on 1 factor. The 2 items that did not fit the 1-factor model were omitted from further testing. All 9 items on the sports subscale loaded on 1 factor. The coefficient alpha values were .96 and .95 for the ADL and sports subscales, respectively. The errors associated with a single measure were +/-4.6 and +/-3.8 points for the ADL and sports subscales, respectively. Item response theory found that all items contributed to their test information curves and were potentially responsive. The correlations between the HOS and Short Form 36 measures of physical function were significantly different than their correlation to measures of mental functioning (P < .005). CONCLUSIONS: The results of this study provide evidence of validity to support the use of the HOS ADL and sports subscales for individuals with labral tears. This includes individuals who underwent arthroscopic surgery, as well as those who did not. Specifically, the results of this study found that the HOS ADL and sports subscales were unidimensional, had adequate internal consistency, were potentially responsive across the spectrum of ability, and contributed information across the spectrum of ability. In addition, scores obtained by the HOS related to measures of function and did not relate to measures of mental health. LEVEL OF EVIDENCE: Level III, development of diagnostic criteria with nonconsecutive patients.