This study examined the measurement properties of the AUSCAN Osteoarthritis Hand Index in a large, community-based sample. Prior studies have confirmed the validity of this scale in clinical and family-based samples, all with radiographic hand OA1–5
. Results of this study extend knowledge regarding the AUSCAN's validity in a more general population, as well as across demographic and clinical subgroups. We observed high levels of internal consistency, both for the total AUSCAN score and the subscales. Furthermore, internal consistency was acceptable for all subgroups we examined, including individuals without self-reported hand pain and individuals without radiographic hand OA. Cronbach's alphas for the total scale and subscales were above 0.90. This may indicate some item redundancy, and it is possible that the number of items could be reduced. Similar to prior results among a sample of individuals with familial hand OA5
, we found strong correlations among the AUSCAN subscales, particularly pain and function (r
= 0.81). This is likely due to similarity between some activities queried in the pain and function subscales (i.e., turning objects, squeezing/wringing).
Results of this study also support the construct validity of the AUSCAN subscales. Specifically, the grip and pinch strength were more strongly associated with the AUSCAN function subscale than the pain and stiffness subscales. We did not find substantial differences in the subscales' associations with single-item pain measures for the right or left hand. This may be partly due to the fact that these hand pain items have a limited distribution (scale of 0–3) and may not be sensitive to small differences in pain. Our previous work showed that among a sample of individuals who all had hand OA, the same single-item pain measure was more highly correlated with the AUSCAN pain subscale than with the AUSCAN stiffness and function subscales5
. Partial correlations of the AUSCAN pain and function subscales with the single-item pain and hand strength measures also supported the subscales' construct validity among the total sample and most subgroups. In these analyses, the single-item pain measure was more strongly associated with the AUSCAN pain subscale than the function subscale, except among individuals in the middle age group (55–64; in which the correlation with the AUSCAN function subscale was very slightly higher) and those without radiographic hand OA (in which these associations were approximately equal). This may indicate some weakness in the construct validity and specificity of the AUSCAN pain subscale among these subgroups. However, as stated above, it also may be related to limitations in our single-item hand pain measures.
The exploratory factor analysis of the AUSCAN indicated a one factor model best fit the data. This suggests there may be some item overlap between the subscales. However, our factor analysis with two factors specified supported the intended subscale structure of the AUSCAN for the total sample and most subgroups we examined. Specifically, all pain items loaded on one factor and all function items on another. There was a minor deviation from this pattern for the subgroup of patients who reported that they did not have current hand pain on the single-item measure. For this group, one item (“pain at rest”) did not load on either factor. This is likely because the majority of individuals in this subgroup do not have current hand pain at rest. However, overall results of this study do not show any major problems with the validity or utility of the AUSCAN for this subgroup of individuals.
Among African Americans, there was a more notable difference in the factor structure of the AUSCAN pain and function items when two factors were specified. Three of the items on the function subscale loaded on a factor with the five pain subscale items. These results suggest that for African Americans, the AUSCAN pain and function subscales may not measure two discrete domains of pain and function as expected. Prior research on the Western Ontario McMaster University Osteoarthritis Index (WOMAC), an index of lower extremity pain, stiffness, and function18
, indicated that scale items clustered according to the type of activity, rather than according to pain, stiffness, and function subscales19,20
. However, we did not observe a clear factor pattern corresponding to activity type in this analysis. The function items that loaded on the factor with the pain items relate to tasks that generally require less strength (turning faucets and doorknobs, buttoning) than the remainder of the function items that loaded on a factor together (i.e., opening a jar, carrying full pot, picking up large, heavy objects). However, it is not clear why the less difficult function items share more variance with the pain items (which relate to tasks of varying difficulty) than with the other function items. Differential item functioning analysis may help to identify how AUSCAN items perform across racial groups21
. Cognitive interviewing would also help to examine individuals' thought processes when responding to these items. This may be particularly useful for the pain items, such as “gripping”, “lifting”, “turning”, and “squeezing” that do not indicate a specific level of task difficulty as the function items do (i.e., “picking up large, heavy objects”). There may be individual differences in the types and difficulty of tasks that individuals think about when responding to pain items (i.e., pain when lifting a heavy item or a light item). It would be valuable to examine whether these cognitive processes vary according to race and other demographic characteristics.
The racial differences observed in this study add to prior research showing that African Americans and whites differ in their experience and descriptions of pain7,22
. The potential impact of this differing factor structure of the AUSCAN among African Americans is not clear from these analyses and warrants further research. Because the subscales may not discretely measure pain and function as expected, their sensitivity to change may not be optimal when used independently (rather than as part of a total AUSCAN score). Longitudinal studies are needed to assess the AUSCAN subscales' ability to detect change in this demographic group. In addition, further research is needed to understand factors underlying racial differences in self-reported hand pain and function. It is possible that the observed racial difference may be attributed to social or cultural factors rather than being a “true” racial difference.
In summary, results of this study support the validity of the AUSCAN in a community sample composed of adults with and without OA. While the AUSCAN was originally designed and validated for use among individuals with radiographic hand OA, this study indicates its utility may be broader, suitable for assessing hand pain, stiffness, and function in more general adult samples. This study also supported the AUSCAN's construct validity and factor structure among men, women, and Caucasians separately, though there are questions about the factor structure among African Americans. Overall, results suggest that the AUSCAN has acceptable measurement properties and can be a valuable tool for assessing the impact of OA on pain and function in the community.