To those who believe the Scientific Method is one of last objective defenses against lies, the type of analysis done is incredibly important. It’s about the hierarchy of medical evidence. On the lowest tier is a Review Article, which this is. These can be helpful and informative, but the approach is to assemble already available data. To answer your question, a prospective, randomized clinical trial with a large number of subjects is the most impactful evidence. And, I don’t need one, because a Danish one was already done last year on the useless of masks - Bundgaard et al Annals of Internal Medicine 2020