Effect of risk adjustment method on comparisons of health care utilization between complementary and alternative medicine users and nonusers

Objectives: Complementary and alternative medicine (CAM) providers are becoming more integrated into the United States health care system. Because patients self-select CAM use, risk adjustment is needed to make the groups more comparable when analyzing utilization. This study examined how the choice of risk adjustment method affects assessment of CAM use on overall health care utilization. Design and subjects: Insurance claims data for 2000-2003 from Washington State, which mandates coverage of CAM providers, were analyzed. Three (3) risk adjustment methods were compared in patients with musculoskeletal conditions: Adjusted Clinical Groups (ACG), Diagnostic Cost Groups (DCG), and the Charlson Index. Relative Value Units (RVUs) were used as a proxy for expenditures. Two (2) sets of median regression models were created: prospective, which used risk adjustments from the previous year to predict RVU in the subsequent year, and concurrent, which used risk adjustment measures to predict RVU in the same year. Results: The sample included 92,474 claimants. Prospective models showed little difference in the effect of CAM use on RVU among the three risk adjustment methods, and all models had low predictive power (R² ≤0.05). In the concurrent models, coefficients were similar in direction and magnitude for all risk adjustment methods, but in some models the predicted effect of CAM use on RVU differed by as much as double between methods. Results of DCG and ACG models were similar and were stronger than Charlson models. Conclusions: Choice of risk adjustment method may have a modest effect on the outcome of interest.