This is reasonable but doesn’t excuse us not running experiments.
For example, suppose there’s a varying Health factor (how much sleep, overtraining, stress, nutrition, etc) and that if you’re above a threshold you will not succumb to exposure at some proximity no matter the duration. If this were true (I don’t think it is, but we need experiments to know), then Bob would be less likely to get sick if his Health has enough daily variation.
This is reasonable but doesn’t excuse us not running experiments.
For example, suppose there’s a varying Health factor (how much sleep, overtraining, stress, nutrition, etc) and that if you’re above a threshold you will not succumb to exposure at some proximity no matter the duration. If this were true (I don’t think it is, but we need experiments to know), then Bob would be less likely to get sick if his Health has enough daily variation.
That is, in fact, one of the variances that is disregarded by the question since “everything else about the risk factors is constant”