Because there was no plausible reason why the 2 groups would differ in outcomes before the initiation of an atypical antipsychotic drug, we reasoned that null associations would enhance assertions that the 2 groups were similar in baseline risk for the study outcomes.
We did all analyses with SAS, version 9.3 (SAS Institute).
In all outcome analyses, we interpreted 2-tailed P values less than 0.05 as statistically significant.