Gary, I did not re-read where you are quoting from, but association does not prove cause and effect.
For example. Those taking analgesics before hiking may have had prior headache or AMS history, other medical issues, age, etc. In other words, were they are fair comparison to the control group? (assuming their was an accurate control group.) A good study would try to take that into account. OTOH, did those taking analgesics start pills not chronically before the hike, but at the start or early into it? If so, maybe they knew from past history that they might benefit from it (for what little good it does). Again, a well designed study would take this into account.
Ken can better answer this as he has been part of an AMS study on Whitney.
