No, I’m not sure how strong the selection effects are. In fact it’s seems certain that some selection effects exist, and I don’t know how to estimate them. But the signal is so strong that I didn’t think selection effects could explain all of it. It might be an interesting question to investigate. Presumably there are studies done on making out-of-shape people exercise. Military recruiting and training could also provide a lot of data.
No, I’m not sure how strong the selection effects are. In fact it’s seems certain that some selection effects exist, and I don’t know how to estimate them. But the signal is so strong that I didn’t think selection effects could explain all of it. It might be an interesting question to investigate. Presumably there are studies done on making out-of-shape people exercise. Military recruiting and training could also provide a lot of data.