Randomization and Masking
BLIND
The participants were randomly assigned in a 1:1 ratio to the intervention and placebo groups, respectively. Randomization was performed through a central, password-protected, web-based system with an audit trail that has been used for several prior international studies. Randomization was stratified by site in permuted blocks of size 4. The randomization list was prepared by the trial statistician (A.G.D.) who did not disclose the block size until after study enrollment was complete. Access to unblinded data was limited to the independent data monitoring committee until the trial database was completed and locked. Outcomes were not examined by treatment assignment until after the statistical analysis plan was finalized and published. To blind patients, investigators, and health care practitioners, selenium and placebo were prepared and supplied by an industry partner (Biosyn) in a way to maintain blinding. Selenium and placebo were provided similar in appearance, consistency, volume, and smell; study researchers were blinded to the treatment assignment at the time of enrollment to exclude selection bias.