Don’t disregard base rates!

We are bad at working with probabilities, as a species. If you read that a drug makes you 50% less likely to have a Brain Aneurysm, that doesn’t necessarily mean that it’s worth whatever costs and side effects It has. Brain aneurysms are already incredibly rare. It’s true that you’re 10x as likely to win the lottery if you buy ten tickets, but more practically speaking all you’ve done is waste 10x as much money.

If you think you might have a disease that has a 0.005% prevalence in the population. You test for it and test positive. The tests are 95% chance accurate. You’re still MUCH MORE LIKELY to NOT have the disease than to have it. (This is an application of Bayes Theorem)

Examples

Prostate cancer - you’re more likely to die with it, than die of it. Removing the Prostate is a serious surgery that will rob you of time now (Getting the procedure & recovering) and the quality of life you’ll give up (due to side effects). Roll the dice, 12 means you die sooner, but 2 through 11 mean you’re not hassled with any of these things.


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