Systems and small probabilities

I read an article from some scientist who was very much against masks and the belief that they helped prevent the spread of Covid-19. His argument was that masks didn’t do anything, and were more of a comfort blanket. They were something governments mandated to show that they were “doing something”.

The Covid-19 virus, according to him, was too small, and isn’t just passed through droplets that can be caught by masks, but through air. And these Covid-19 aerosols will pass through the holes on most masks like a cat through an open door beyond which no humans are (analogy’s terrible and it’s mine but the point’s the same).

I’m no expert on masks, or aerosols (or cats) but do think he may have a point.

And yet, in practice, I think we’re seeing that masks do work to reduce Covid-19 infection rates.


There are confounding variables no doubt. Governments don’t typically issue mask mandates standalone. Mask mandates typically come with other directives like social distancing, restricted travel, and work from home orders. These help too.


I’d like to share my thoughts on this.

For context: I took some courses in systems theory (introductory) as well as statistics (intermediate). I also have experience wearing a mask (advanced).


Let’s assume mask wearing doesn’t do anything — that it has a zero percent efficacy rate.

But wearing a mask impacts other behaviours — it’s benefits do not stem from keeping viruses in or out alone.

And that scientist didn’t quite address that.

I’m going to list a few things that wearing a mask impacts, and a guesstimate of their efficacy in the following points in brackets:

  • Speaking through a mask is a pain. I feel muffled and like I’m speaking into a pillow. I speak less. I avoid unnecessary conversation. I go out less. (~20% impact)
  • When I wear a mask, I don’t feel like things are “normal”. I feel like there’s a pandemic going on. Which makes me a little more cautious around people. When I do go out, I walk a little further from others; I avoid the more crowded areas; and I look for places with better ventilation and aren’t enclosed.(~10%)
  • Wearing a mask, I don’t quite recognise people as easily — everyone looks the same — and when I do, I wave instead of say hello and stop to chat. (~5%)
  • Other people think the same way as me and go out less and speak less and see friends and acquaintances less, so there are fewer people out there potentially getting sick and spreading anything. (~25%)

I think even if masks do nothing on their own, we’re still getting quite a bit of benefit. These small probabilities add up.

What is more, we don’t really need 100% efficacy or even 50% efficacy to prevent a virus from going viral (ha-ha), as long as we don’t cross a critical threshold of virulence (whatever that is) we’ll be OK.


So yes, masks maybe useless at keeping out viruses (or more accurately in the case of Covid-19 keeping it in).

But no, I don’t think they’re useless.

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