I’m not sure what distinction you’re making when you say someone might believe both of
putting on sunscreen has a statistical tendency to make people stay out in the sun longer, which is net negative wrt skin cancer
all else being equal, putting on sunscreen is net positive wrt skin cancer
If the first means only that being out in the sun longer is negative then of course it’s easy to believe both of those, but then “net negative” is entirely the wrong term and no one would describe the situation by saying anything like “wearing sunscreen actually tends to increase risk of skin cancer”.
If the first means that the benefit of wearing sunscreen and the harm of staying in the sun longer combine to make something net negative, then “net negative” is a good term for that and “tends to increase risk” is fine, but then I don’t understand how that doesn’t flatly contradict the second proposition.
Sorry, here’s another attempt to convey the distinction:
Possible belief #1 (first bullet point):
If we perform the causal intervention of getting someone to put on sunscreen, then (on average) that person will stay out in the sun longer; so much so that the overall incidence of skin cancer would be higher in a randomly selected group which we perform that intervention on, in comparison to a non-intervened group (despite any opposing beneficial effect of sunscreen itself).
I believe this is the same as the second interpretation you offer (the one which is consistent with use of the term “net”).
Possible belief #2 (second bullet point):
If we perform the same causal intervention as in #1, but also hold fixed the time spend in the sun, then the average incidence of skin cancer would be reduced.
This doesn’t flatly contradict the first bullet point, because it’s possible sunscreen is helpful when we keep the amount of sun exposure fixed, but that the behavior changes of those with sunscreen changes the overall story.
OK, yes: I agree that that is a possible distinction and that someone could believe both those things. And, duh, if I’d read what you wrote more carefully then I would have understood that that was what you meant. (”… because when giving advice they tend to model the other person as virtuous enough to overcome the temptation to stay out in the sunlight longer.”) My apologies.
I’m not sure what distinction you’re making when you say someone might believe both of
putting on sunscreen has a statistical tendency to make people stay out in the sun longer, which is net negative wrt skin cancer
all else being equal, putting on sunscreen is net positive wrt skin cancer
If the first means only that being out in the sun longer is negative then of course it’s easy to believe both of those, but then “net negative” is entirely the wrong term and no one would describe the situation by saying anything like “wearing sunscreen actually tends to increase risk of skin cancer”.
If the first means that the benefit of wearing sunscreen and the harm of staying in the sun longer combine to make something net negative, then “net negative” is a good term for that and “tends to increase risk” is fine, but then I don’t understand how that doesn’t flatly contradict the second proposition.
What am I missing?
Sorry, here’s another attempt to convey the distinction:
Possible belief #1 (first bullet point):
If we perform the causal intervention of getting someone to put on sunscreen, then (on average) that person will stay out in the sun longer; so much so that the overall incidence of skin cancer would be higher in a randomly selected group which we perform that intervention on, in comparison to a non-intervened group (despite any opposing beneficial effect of sunscreen itself).
I believe this is the same as the second interpretation you offer (the one which is consistent with use of the term “net”).
Possible belief #2 (second bullet point):
If we perform the same causal intervention as in #1, but also hold fixed the time spend in the sun, then the average incidence of skin cancer would be reduced.
This doesn’t flatly contradict the first bullet point, because it’s possible sunscreen is helpful when we keep the amount of sun exposure fixed, but that the behavior changes of those with sunscreen changes the overall story.
OK, yes: I agree that that is a possible distinction and that someone could believe both those things. And, duh, if I’d read what you wrote more carefully then I would have understood that that was what you meant. (”… because when giving advice they tend to model the other person as virtuous enough to overcome the temptation to stay out in the sunlight longer.”) My apologies.