Yes, masks reduce the risk of spreading COVID, despite a review saying they don’t

 https://www.gavi.org/vaccineswork/yes-masks-reduce-risk-spreading-covid-despite-review-saying-they-dont

The review starts with an assumption that masks provide respiratory protection, which is flawed. An understanding of these differences should inform both studies and reviews of those studies.

The authors of the Cochrane Review acknowledged compliance with masking advice was poor in most studies. In the real world, we can’t force people to follow medical advice, so RCTs should be analysed on an “intention to treat” basis.

For example, people who are prescribed the active drug but who choose not to take it should not be shifted to the placebo group for the analysis. But if in a study of masking, most people don’t actually wear them, you can’t conclude that masks don’t work when the study shows no difference between the groups. You can only conclude that the mask advice didn’t work in this study.