Comment by seasoup

What this study shows is that when infection rates are high people wear masks, and conversely, that when people wear masks infection rates are high. Or put another way, it either shows that high infection rates cause people to wear masks, that wearing masks causes high infection rates, or that neither causes the other but some tertiary value not part of the study causes both to rise and fall in tandem.

It does not effectively demonstrate the amount that wearing a mask raises, or reduces, infection rates.