smoking and hormone supplementation are by no means independent variables when studying cancer risk. You might normalize for them by only comparing smokers with smokers or oral contraception users w other oral contraception users, but a study like that gets very complex when you have to compare smokers who exercise but use oral contraception, don't drink and are vegetarian vs smokers who exercise but use oral contraception, don't drink and are omnivores and I see no indication in the article that any of these variables were normalized for.I think you're right, the second paragraph is a warning and the word "impossible" was chosen deliberately.
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smoking and hormone supplementation are by no means independent variables when studying cancer risk. You might normalize for them by only comparing smokers with smokers or oral contraception users w other oral contraception users, but a study like that gets very complex when you have to compare smokers who exercise but use oral contraception, don't drink and are vegetarian vs smokers who exercise but use oral contraception, don't drink and are omnivores and I see no indication in the article that any of these variables were normalized for.I think you're right, the second paragraph is a warning and the word "impossible" was chosen deliberately.