High dimensional propensity scores
We estimated high dimensional propensity scores for all patients at each site. The high dimensional propensity score algorithm is available as downloadable SAS software files from the Brigham and Women’s Hospital.17 As described in detail elsewhere,18 the algorithm prioritises thousands of drug, diagnostic, procedure, and demographic variables according to their potential to cause bias in the estimate of an exposure-outcome association (such as rate ratio). Typically, the 200-500 variables most likely to cause bias are included in a propensity score model that is estimated using logistic regression. In our analysis, we used high dimensional propensity scores to estimate the predicted probability (propensity score) of exposure to higher potency statins versus lower potency statins, conditional on all of the included covariates.
In addition to the 500 covariates empirically selected for the propensity score models, we also included the following pre-specified covariates: year of cohort entry and, from the year preceding cohort entry, binary indicator variables for whether the patient was hospitalised, had a laboratory test, received more than four distinct prescription drugs dispensed, received a loop diuretic, had more than four physician visits, or had a diagnosis for hypertensive disease, hypercholesterolemia, peripheral vascular disease, or congestive heart failure. After estimating propensity scores, we trimmed from the analysis the patients with the smallest 5% and largest 5% of propensity scores.