Background: To compare serious illness programs (SIPs) using recently developed patient experience measures, adjustment must be made for patient characteristics not under control of the programs. Objectives: To develop a case-mix adjustment model to enable fair comparison of patient experience between SIPs by investigating the roles of patient characteristics, proxy response, and mode of survey administration (mail-only vs. mail with telephone follow-up) in survey responses. Methods: Using survey data from 2263 patients from 32 home-based SIPs across the United States, we fit regression models to assess the association between patient-level variables and scores for seven quality measures (Communication, Care Coordination, Help for Symptoms, Planning for Care, Support for Family and Friends, and two global assessments of care). Characteristics that are not consequences of the care the program delivered were considered as adjustors. Results: Final recommended case-mix adjustors are age, education, primary diagnosis, self-reported functional status, self-rated physical health, self-rated mental health, proxy respondent use, and response percentile (a measure of how soon a person responded compared with others in the same program and mode). Age, primary diagnosis, self-rated mental health, and proxy respondent use had the most impact on program-level scores. We also recommend adjusting for mode of survey administration. We find that up to 12 percent of pairs of programs would have their rankings reversed by adjustment. Conclusions: To ensure fair comparison of programs, scores should be case-mix adjusted for variables that influence patients' reports about care quality, but are not under the control of the program administering care.
Keywords: case-mix; patient experience; patient surveys; serious illness care.