Risk adjusting rehabilitation outcomes: an overview of methodologic issues.

The complexity and mix of rehabilitation patients varies across clinicians and institutions. Comparisons of outcomes across providers must therefore adjust for differences in risk factors across patient populations. Research on risk adjustment has generally focused on acute care hospital outcomes, although techniques for risk adjusting financial outcomes are fairly well developed in rehabilitation, primarily to support Medicare and other prospective payment systems. This article reviews important methodologic issues in risk adjusting rehabilitation outcomes in observational studies of routine clinical practice or for management, such as assessing quality or costs of care. Risk adjusting rehabilitation outcomes is more difficult than risk adjusting other clinical results, such as outcomes of many acute care services. At the outset, characterizing rehabilitation interventions is frequently difficult. Furthermore, outcomes are diverse and depend on myriad factors, including patients' physical and cognitive abilities, underlying medical diseases, sensory and emotional factors, willingness to participate in care, and supportive environments. No risk-adjustment approach can control for every factor affecting outcomes of care. Knowing which risk factors are missing helps guide interpretation of the results and determines how well risk-adjusted outcomes fairly compare providers or treatments.