Yes, I meant exactly a 1 year effect and a random 5 year window and I should have spelled that out. Cancer and many autoimmune diseases take years to notice.
And Jim is right that my example is poor because a prenatal effect pinpoints when the exposure must have occurred. But, actually, I believe that such simple studies don’t find an effect for the normal variation in flu (3% some years, 15% others), except for the 1918 cohort. The studies that find an effect rely on asking the mother if she had flu during pregnancy (which has some post hoc problems).
Yes, I meant exactly a 1 year effect and a random 5 year window and I should have spelled that out. Cancer and many autoimmune diseases take years to notice.
And Jim is right that my example is poor because a prenatal effect pinpoints when the exposure must have occurred. But, actually, I believe that such simple studies don’t find an effect for the normal variation in flu (3% some years, 15% others), except for the 1918 cohort. The studies that find an effect rely on asking the mother if she had flu during pregnancy (which has some post hoc problems).