That’s because this isn’t a “study”, it’s a review. A review introduces no new information - it summarizes the existing literature. This is the meta-review co

That’s because this isn’t a “study”, it’s a review. A review introduces no new information - it summarizes the existing literature. This is the meta-review commissioned by the WHO to investigate the value of PPE, and it is notable because it aggregates a number of low-quality studies and attempts to statistically re-weight their data to arrive at a broader conclusion. It’s notable for face masks, in particular, because it mixes data from hospital settings with community settings, along with respirators and surgical masks, source control and PPE, and attempts to draw a conclusion about “protectiveness” overall.