Rolling the Covid19 dice

The human brain is really good for some things, but not so much at others. For instance, the human brain is exceptionally good at pattern recognition as in the case of spotting a lion waiting to pounce. It’s easy to see why: going back to our very distant ancestors, if they were slightly better at spotting danger hidden in the tall grass they would gain a selective advantage and be more likely to produce offspring, thus passing on their improved skill to their offspring.

However, the human brain sucks at abstract risk assessment in situations like surviving a global pandemic. Not only are we incapable of grasping the risk, we don’t even ask the right questions.

What are the chances of a healthy person dying from Covid-19?

According to OurWorldData.org there’s a 0.9% chance of a person with no pre-existing conditions dying if they catch Covid-19. To simplify the math let’s round that up to 1.0%. That’s one chance in 100.

One chance in one-hundred feels pretty unlikely. You might think you can live, or more accurately die, with that level of risk. But for comparison the average person experiences about a one in one-million chance of dying from non-natural causes each day: electrocution, car accident, slipping in the tub, that sort of thing.

Therefore, if you catch Covid-19 your chances of dying just increased 10,000 fold. To put that in perspective that’s equal to the chances of dying in an accident over the span of 27.4 years. Let’s say that again, if you’re healthy and have no pre-existing conditions and you catch Covid-19 then you’re going to experience 27.4 years of risk crammed into just the next two or three weeks.

Spreading the risk

That’s far from the end of the story. What if you live in a family of four and you pass Covid-19 on to your entire family? I’m not saying that’s a certainty, but if one person in a household becomes infected then the other members are at a very high risk of infection as well. So let’s just go with 100%, you all come down with it. Again, assuming everyone is healthy you now have 4 people with Covid-19. What are the chances that just one of your family members will die?

Now we’re getting into solving some probability equations so I’ll give you an analogy first: each member in your family of 4 is going to roll a die; what is the probability that at least one of you will roll a 6?

The way to approach this problem is to calculate the compliment: what is the probability that no one rolls a 6? Figure that out and subtract from 1.

The probability of something happening equals one minus the probability of it not happening.

For each roll of the die there is a 5/6 chance that it will not be a 6. The four rolls are independent of each other so the answer is (5/6)4 = 54 / 64 = 625 / 1296. Therefore, the probability of rolling at least one six is 1 –  (625 / 1296 ) .517. (Source material)

The chances of someone in a family of 4 healthy people dying of Covid-19 (assuming everyone becomes infected) is similar to the dice problem above where we substitute 1/100 as the probability.

Again, calculate the compliment: the probability of not dying.

(99/100)4 = 994 / 1004 = 96059601 / 100,000,000 0.9605.

Therefore the final probability that someone in a family of 4 dies is:

1 – ( 96059601 / 100,000,000 ) 0.039

Or about 4%

4%

That’s 1 chance in 25!!!

Stop and think about that for a second.

You might think that number is a little too high. You know what? Maybe you’re right. We did round the mortality rate for healthy people up by a tenth of a percent. And maybe it’s even lower for children. Again, no argument here. If it makes you feel better you can halve that probability to 2%. There there, don’t you feel better now? There’s only a 2% chance of someone in your family of 4 dying. Sleep well.

But remember, in this calculation we’re only talking about dying. The probability that someone in your family is going to experience the worst flu-like experience of their lives is much, MUCH, higher. According to the WHO, “Around 1 in every 5 people who are infected with COVID-19 develop difficulty in breathing and require hospital care.”

I’ll save you the math but in a family of 4 the probability that one of you will end up in the hospital is around 59%.

There’s a 59% chance that either you, or one of your loved ones, is going to be wiping fever induced sweat from a loved one’s forehead while silently praying they take one more breath, breath after breath, for a week or more.

Just don’t get infected

You can avoid all of this trauma and just don’t get infected in the first place. Don’t do anything in public that isn’t essential. You don’t have to eat out; you don’t have to go to the movies; you don’t have to…

If you do need to go out in public then cover up, twice. I wear a an N99 mask and a cloth mask over that. Masks are best at preventing an infected person from spreading the virus, not as great at keeping you from getting it.

They say you should keep a 6 foot social distance. How about make that as far as possible. And duration of exposure matters. If you pass an infected person on the street who’s not wearing a mask then your chances of catching the virus is really low, but if you sit next to them for 4 hours on a flight then the probability goes way up.

You’re rolling the dice every time you’re exposed. The best way to play this game is to roll the dice as infrequently as possible.

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