If the baseline is a 30% chance of dying of heart disease and it told you that you had a 70% chance, what would you do differently? (but it won’t.) Probably you should already be doing it because 30% is a big number!
That line of argument is flawed because actions have costs.
To give a simple example (and discussing whether it’s precisely correct is besides the point), you can take baby aspirin to reduce the risk of heart attacks. Aspirin is a blood thinner, it makes clots (which cause heart attacks) less likely. However decreasing coagulation is not an unmitigated blessing. If you get internal bleeding—e.g. a blood vessel ruptured in your brain—that aspirin you’ve been taking could make things significantly worse. It’s a trade-off.
Given this, you want to know on which side (basically, heart attacks vs. strokes) is your personal risk the highest. It is actionable knowledge.
an 80% chance of breast cancer, which is really not that different from a 20% chance
Looks very different to me—you are quite cavalier with a fourfold difference in odds...
4 is a small number. It is pretty rare that a cost-benefit calculation cares about that factor of 4, that multiplying the benefits by 4 will change the decision from reject to accept.
That line of argument is flawed because actions have costs.
To give a simple example (and discussing whether it’s precisely correct is besides the point), you can take baby aspirin to reduce the risk of heart attacks. Aspirin is a blood thinner, it makes clots (which cause heart attacks) less likely. However decreasing coagulation is not an unmitigated blessing. If you get internal bleeding—e.g. a blood vessel ruptured in your brain—that aspirin you’ve been taking could make things significantly worse. It’s a trade-off.
Given this, you want to know on which side (basically, heart attacks vs. strokes) is your personal risk the highest. It is actionable knowledge.
Looks very different to me—you are quite cavalier with a fourfold difference in odds...
4 is a small number. It is pretty rare that a cost-benefit calculation cares about that factor of 4, that multiplying the benefits by 4 will change the decision from reject to accept.
It seems we have a different perception of smallness and tend to encounter different cost-benefit calculations.