Abstract
BACKGROUND: To evaluate the utility of the Impact Stratification Score (ISS) in characterizing health-related disease burden for older adult patients with multiple chronic conditions (MCC). METHODS: The sample of 1226 older adult MCC patients (average age of 80, 51% female, and 89% White) completed the PROMIS-29 v2.1 profile that contains the 9 ISS items. The ISS was examined using factor analysis (i.e., correlated factors and bifactor models). We evaluated the relative validity of ISS compared with other PROMIS-29 scores using ratio of F-statistics from multivariate regressions predicting each PROMIS-29 score from patient chronic conditions and utilization patterns. RESULTS: Bifactor model results indicated essential unidimensionality, primarily reflecting one general construct (i.e., impact) and that, after accounting for impact, very little reliable variance remained in the two group factors. General impact scores were reliable (omegaH =.73). ISS scores were significantly higher according to older age, female gender, and Hispanic ethnicity, increased with increasing number of chronic conditions, and were strongly related to presence of most chronic conditions and healthcare utilization rates. Relative efficiency coefficients revealed that ISS scores were more strongly related to most chronic conditions relative to PROMIS pain intensity, physical health, and pain interference scores and outperformed the PROMIS-29 physical health summary score for several conditions including arthritis, diabetes, and high blood pressure. CONCLUSION: This study presents evidence that the ISS is a sufficiently unidimensional and reliable measure that may be useful in characterizing health-related disease burden among older adult ambulatory patients with two or more chronic conditions.