Re:A hot bath has benefits similar to exercise
by brutos on Tuesday March 21, 2017 @03:15AM
(#13920387)
These studies are usually done as cohort studies. Meaning the study group shares a defining trait (such as the same date of birth).
Obviously this is not as great as a double-blind study. But you can't let one group do real exercise and the other one placebo exercise. So the cohort study is probably the best possible study design in this case.
The people doing these studies try very hard to minimize biases (sometimes failing, but ruling out every possible biases is hard).
Self-selection can completely override other well-understood mechanisms...