Probability and decision-making
A good friend is delaying having COVID vaccine as she’s worried about the clots. I’m writing this up for her.
If there are two dices, one is normal with 1 to 6 on each side and the other with 1, 1, 3, 3, 6, 6 on each side, the probability of getting 6 from throwing the normal dice is 1/6 or 17% and the other dice is 1/3 or 33%. Let’s say, we are forced to play the game of throwing a dice, but we can choose which dice to throw. The rule of the game is that we win if the dice turns 6 and we lose for other numbers.
The question is which dice we would choose to throw and we want to win? The 17% or 33% dice.
Logic dictates we should choose the 33% dice because there’s higher chance of getting 6. We are more likely to win with this dice.
Making a decision to get Astra vaccine is the same.
The comparison is between probability of death from vaccine adverse effects and probability of getting COVID and die. We are forced to choose between these two probabilities and scenarios. In reality, there’s no such scenario where the probability of getting COVID and die is 0. That means if you chose not to get Astra vaccine, the risk of you dying from blood clot may be 0, but the risk of you dying from COVID would be multiple times higher than the risk of you dying from Astra vaccine.
COVID is new, vaccines are new, all of these are evolving situations. New info continuously emerges i.e. things could change, recommendations could change, but we can only base our decisions on what has already happened. And what has happened so far is the risk of dying from COVID in people older than 50 is a lot higher than the risk of dying from Astra vaccine.
We can say we read from somewhere, we heard from someone or even we see our friends suffer from vaccine adverse effects, but it means absolutely nothing because we don’t see all the millions and millions of people who have had the vaccine. If we made our decisions base only on what we as an individual have seen, heard and felt, we would discount the large amount of information that we did not see. Just because we didn’t see it, didn’t experience it, doesn’t mean it doesn’t exist. When it comes to probability, the bigger the sample size, the better.
Now what if we want to wait for Pfizer vaccine
Here the comparison will be something like this
1. Probability of dying from Astra vaccine’s adverse effects + dying from Covid after Astra vaccination (vaccine is not 100% effective, people can still get Covid and die after vaccination)
2. Probability of dying from Pfizer vaccine’s adverse effects + dying from Covid after Pfizer vaccination
We should go with whichever option with lower number.
In the game of chance, the best decision and the best outcome are not necessarily the same thing. The best decision is based on available options and rules of probability (as outlined above). The best outcome can happen because of just sheer luck or sheer misfortune. The thing is we cannot control luck or misfortune, but we can understand probability and control our decisions.
Flawed risk perception
Odds of Covid death for 60-69 female Australian is
8.6 in 1m
https://www.health.gov.au/resources/covid-19-deaths-by-age-group-and-sex
https://www.housingdata.gov.au/visualisation/population/australian-population-age-and-sex
12 cases in population of 1.4m
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Odds of death from Astra
https://www.abs.gov.au/articles/covid-19-mortality-0
Odds of TTS is 14 in 1m
Death rate of TTS is 3%
So odds of death from Astra induced TTS in 60-69 female is
0.42 in 1m
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Odds of dying from Covid is 20.5 time more than that of AZ vaccine.
This doesn’t even take into consideration of suffering from Covid symptoms (e.g. breathing difficulty, chest pain, long-term fatigue, brain fog etc.) in case of contracted, but survive. If we quantify suffering through the concept of Quality Adjusted Life Year (which can quantify suffering as partial death) and add that to 20.5 x, I’m certain the number would be even higher.
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Putting risk in perspectives
One in a million = tossing a coin and turns up head 20 times in a row.
Sitting on a chair (due to the likelihood of falling off it) increases your risk of death by approximately 1.3 micromorts (1.3 in 1m).
Driving a car for 400km exposes you to approximately 1 micromort.
Just having a bath increases your risk of death by 0.3 micromorts.
If we are ok with these daily activities, we’ve got to ponder why we feel uneasy toward AZ?
Everything in life has risks and the art of living a good life is to be clear as to when risks are worth taking. Every day we take a bath and drive, we make a trade-off between the risks associated with what we do and our enjoyment of life, even if we are not always perceiving these risks accurately.