VALIDATION DATA

The iHOT-33 is reliable; shows face, content, and construct validity; and is highly responsive to clinical change. However, it is a lengthy instrument comprising 33 separate questions in 4 domains. 

Internal consistency of the iHOT-12NL was  good, with a Cronbach alpha of 0.96 

Test-retest reliability for the iHOT-12 was good, with an intraclass correlation coefficient of 0.89 (95% bootstrapped CI, 0.83 to 0.93).

Principal component analysis of the iHOT-33 for the development data showed that there were at least 4 important components (with eigenvalues <1) that we can loosely associate with the 4 domains of the iHOT-33. This analysis showed that there was some scope to shorten the iHOT-33 while retaining the main properties of the instrument. This was expected, because the iHOT-33 has been deliberately developed with a degree of innate redundancy to provide a measure that is both responsive to change and stable across possibly highly heterogeneous populations. Four items, in order of importance, accounted for 99% of the variability in the overall mean of the 33 items: (1) Overall, how much pain do you have in your hip/groin? (2) How concerned are you about picking up or carrying children because of your hip? (3) How concerned are you about cutting/changing directions during your sport or recreational activities? and (4) How much trouble do you have pushing, pulling, lifting, or carrying heavy objects at work? Reassuringly, these 4 selected items represented 1 item from each of the 4 domains identified in the full iHOT-33 questionnaire.

There is good agreement between the 2 sets of scores, with regression analysis showing that the iHOT-12 accounted for 95.9% (95% CI, 95.0% to 96.8%) of the variation in the iHOT-33. This is close to the result of analysis of the development dataset with a value of greater than 99%.

Standardized effect sizes were 1.03 (95% CI, 0.70 to 1.36) and 0.98 (95% CI, 0.67 to 1.28) for the iHOT-33 and iHOT-12, respectively, indicating almost exact equivalence in responsiveness to clinical change for the 2 questionnaires.

iHot-12 shows excellent construct validity (Spearman r = 0.979). The spearman’s correlation coefficient was derived from regression signifying that iHOT-12 accounted for 95.9% of the variation of the iHOT-33.