Comparison of Calipers for Matching on the Disease Risk Score.

Previous studies have compared calipers for propensity score (PS) matching, but none have considered calipers for matching on the disease risk score (DRS). We used Medicare claims data to perform 3 cohort studies of medication initiators: a study of raloxifene versus alendronate in 1-year nonvertebral fracture risk, a study of cyclooxygenase 2 inhibitors versus nonselective nonsteroidal antiinflammatory medications in 6-month gastrointestinal bleeding, and a study of simvastatin + ezetimibe versus simvastatin alone in 6-month cardiovascular outcomes. The study periods for each cohort were 1998 through 2005, 1999 through 2002, and 2004 through 2005, respectively. In each cohort, we calculated 1) a DRS, 2) a prognostic PS which included the DRS as the independent variable in a PS model, and 3) the PS for each patient. We then nearest-neighbor matched on each score in a variable ratio and a fixed ratio within 8 calipers based on the standard deviation of the logit and the natural score scale. When variable ratio matching on the DRS, a caliper of 0.05 on the natural scale performed poorly when the outcome was rare. The prognostic PS did not appear to offer any consistent practical benefits over matching on the DRS directly. In general, logit-based calipers or calipers smaller than 0.05 on the natural scale performed well when DRS matching in all examples.