Statistical Analysis
REGRESSION, SECONDARY, INTERACTION
The primary hypothesis was addressed on an intention-to-treat basis. As a 2 × 2 factorial design, analysis consisted of 2 comparisons: (1) those patients randomized to selenium vs those randomized to the associated placebo, stratifying by vitamin E allocation; and (2) those patients randomized to vitamin E vs those randomized to the associated placebo, stratifying by selenium allocation. Interaction was not expected. Treatment groups were compared by Kaplan-Meier estimates of recurrence-free and progression-free interval; log-rank tests were used to test the hypothesis of no difference between treatments. Hazard ratios (HRs) from Cox proportional hazards regression models compared treatments, both unadjusted and adjusted for known prognostic factors. Similar methods were used for secondary outcomes. These analyses were completed on November 28, 2022.All tests used a 2-sided 