VALIDATION DATA

Cronbach’s alpha was 0.95, 0.93 and 0.93 for the hip, knee and combined samples, respectively.

Cronbach’s alpha was above 0.85 for constant pain and intermittent pain for each of the hip, knee and combined samples.

ICC=0.85 (95% CI 0.76–0.91)

Minimal detectable change: 46.6 (ICOAP pain),  49.6 (ICOAP constant pain), and 50.8 (ICOAP intermittent pain)  (Singh, 2014)

Item generation was performed using standardized focus groups and interviews with open-ended questions. Following these discussions, priorities and concerns of individuals living with hip or knee OA pain were further assessed. Content analysis of resulting transcripts was used to identify themes, which were verified with participants. 

Principle component analysis with varimax rotation to evaluate whether constant and intermittent pain would be best represented by two domains of pain rather than a single construct. In an exploratory analysis using eigenvalue = 1 criteria to consider retaining factors, three factors were extracted that explained 81.7% of the variance (factor 1=54.9%, factor 2=16.8%, factor 3=10.0%). The solution was complex with multiple loadings of >0.40 across factors. Given the complexity of the results from the orthogonal rotation, a solution was also obtained using promax rotation. This solution further confirmed the complexity as all items with the exception of frequency of pain that comes and goes, loaded on multiple factors. Based on these results, subsequent analyses were based on a total summed score for the 11 items.

A Rasch analysis was also performed and the results  supported the use of Constant and Intermittent subscales as unidimensional measures of pain (Moreton, 2012).