remarkably similar to the SIP suggests that the loss of these items did not contribute to substantial losses in convergent validity. are several objectives to pursue in the future with regard to the utility of the SIP-CP. Although measurements in IRT are based on items rather than the sample, there is still a need to ensure the heterogeneity of this sample by testing whether the factor structure of the SIP-CP can be replicated in another large, independent sample of individuals seeking treatment for chronic pain. Formal testing of the local independence assumption for dimension scores should examine whether there are highly similar or highly correlated items across subscales, while testing for parameter invariance by examining differential item functioning across groups (by age, sex, socioeconomic status, pain duration, etc.) would further establish whether the SIP-CP can be applied to a broader population of individuals with chronic pain. Sensitivity to treatment-related change, a strength of the original SIP, should also be examined in the SIP-CP. In addition, the SIP-CP does not include item weights, as those used in the SIP were based on expert judgment, rather than empirical inquiry. Further efforts to determine and test empirically supported item weights, like those generated through IRT methods by Lindeboom and colleagues (2004), may be of use. Finally, tests examining the relative utility of the SIP-CP in relation to other measures of disability may be informative. For example the SF-36 (Ruta, Garratt, Abdalla, Buckingham, & Russell, 1993) and US National Institutes of Health-sponsored PROMIS Pain Interference (Amtmann et al., 2010) measures, along with many other options, are available and it is not clear that the item burden of the SIP-CP, which is greater than most other available measures, offers more useful or broad information with regard to assessing changes in individual patient functioning. Our clinical experience suggests that the SIP (and now SIP-CP) provides a richer source of information and stands to offer greater utility clinical and research endeavors, but future work will have to evaluate the accuracy of those observations empirically.
remarkably similar to the SIP suggests that the loss of these items did not contribute to substantial losses in convergent validity. are several objectives to pursue in the future with regard to the utility of the SIP-CP. Although measurements in IRT are based on items rather than the sample, there is still a need to ensure the heterogeneity of this sample by testing whether the factor structure of the SIP-CP can be replicated in another large, independent sample of individuals seeking treatment for chronic pain. Formal testing of the local independence assumption for dimension scores should examine whether there are highly similar or highly correlated items across subscales, while testing for parameter invariance by examining differential item functioning across groups (by age, sex, socioeconomic status, pain duration, etc.) would further establish whether the SIP-CP can be applied to a broader population of individuals with chronic pain. Sensitivity to treatment-related change, a strength of the original SIP, should also be examined in the SIP-CP. In addition, the SIP-CP does not include item weights, as those used in the SIP were based on expert judgment, rather than empirical inquiry. Further efforts to determine and test empirically supported item weights, like those generated through IRT methods by Lindeboom and colleagues (2004), may be of use. Finally, tests examining the relative utility of the SIP-CP in relation to other measures of disability may be informative. For example the SF-36 (Ruta, Garratt, Abdalla, Buckingham, & Russell, 1993) and US National Institutes of Health-sponsored PROMIS Pain Interference (Amtmann et al., 2010) measures, along with many other options, are available and it is not clear that the item burden of the SIP-CP, which is greater than most other available measures, offers more useful or broad information with regard to assessing changes in individual patient functioning. Our clinical experience suggests that the SIP (and now SIP-CP) provides a richer source of information and stands to offer greater utility clinical and research endeavors, but future work will have to evaluate the accuracy of those observations empirically.