There is relatively little empirical research on the quality of home health care (Institute of Medicine, 2001). Important exceptions include the work of the team at the University of Colorado responsible for developing OBQI under contract to CMS. The method used by CMS to risk-adjust patient outcomes is logistic regression.2 The initial modeling approach involved conceptually and clinically specifying all possible risk factors that might influence the OBQI outcome from a large number of candidate risk factors derived from the OASIS instrument. The grouping of the potential risk-adjusters by OASIS content area represents a framework for thinking about contributors to patient outcomes. All but the length of stay (LOS) category fit within the five broad categories identified by Iezzoni.
A stepwise logistic regression approach is used to assess the relationship between each candidate risk factor and the outcome measure under consideration. Separate logistic regression models are used for each outcome measure and, in some cases, submodels are estimated for patients with different baseline values of the outcome indicator. For example, three sub-models are estimated when assessing Improvement in Transferring: one for patients who can transfer with minimal human assistance; one for patients who are unable to transfer by themselves but able to bear weight and pivot during the transfer process; and one for patients with higher levels of disability in transferring. Details of the risk-adjustment methodology are provided in Shaughnessy and Hittle (2002) Overview of Risk Adjustment and Outcome Measures for Home Health Agency OBQI Reports available for direct download at http://www.cms.hhs.gov/apps/hha/RiskAdj1.pdf with the risk-adjustment models for the 30 outcomes risk-adjusted in OBQI at http://www.cms.hhs.gov/apps/hha/riskadj1appa.pdf. The risk-adjustment model for Improvement in Pain Interfering with Activity (risk-adjusted in HHQI but not in OBQI reports) is at http://www.cms.hhs.gov/apps/hha/RiskModels.pdf. Risk-adjusted outcomes are reported in a recent analysis of whether home health quality changed following the introduction of the Medicare prospective payment system (Schlenker, Powell and Goodrich, 2005).