The report of this study in the Journal of the American Medical Association describes it as a "double-blind, randomized, placebo-controlled factorial...

The report of this study in the Journal of the American Medical Association describes it as a “double-blind, randomized, placebo-controlled factorial trial.” “Factorial” means that the treatments are formed from more than one factor. What are the factors? What do “double-blind” and “placebo-controlled” mean?