Mask-wearing: the Danish study

This study has gotten some attention, but the media accounts I've seen don't accurately report what it found (this one is typical).  First, the study did not control at all for what participants did and who they were with when not outside the home:  so it is possible that the participants (who wore masks outside the home) lived with folks who never wore masks and/or did careless things that exposed them to infection.  Second, the study also did not control for exposure to non-mask-wearers outside the home.  One possible takeaway from the study is that wearing surgical masks (the masks at issue) is not very effective when you're around others who are not wearing surgical masks as well, which seems plausible.