A naive question that's been bugging me.

Suppose you make a mask out of e.g. a scarf, and it is not 100% effective -- i.e., it is possible for the virus to get through it. Isn't it nevertheless likely to make a difference? And even if it reduced the escape of the virus ... 1/

by only 50%, would it not have a noticeable effect on the reproduction rate if such makeshift masks were widely used?

Part of the reason I ask is that I read a paper that claimed that hospital masks were not effective, and backed up the claim by pointing to experiments ... 2/

showing that it was possible for the virus to escape, or demonstrating the presence of the virus on the outside of masks, etc. All of that seemed consistent with masks being better than nothing, even if not perfect.

If it turns out that putting a scarf over your mouth ... 3/

only stops 5%, say, of your virus-filled droplets escaping into the atmosphere, then maybe it's not worth it. But is that the case? Can anyone give me pointers to literature that addresses the question of whether masks of various types are at least partially effective? 4/4