[bjterry]

There are a mountain of studies that have been done on meditation. Among those that are controlled, there a few different strategies.

The best strategy is an "active control" group which receives some combination of education, attention from instructors, group therapy and the like which is matched with the meditation group for time and attention. This has subsets of "specific active control" in which the control is a known procedure (like exercise or progressive muscle relaxation) or "non-specific active control" in which the control procedure is not a known effective procedure and so is expected not to have any effect.

The other main control group used is a "wait list" or "usual care" control, in which the participants don't receive any treatment or only receive the treatment you would usually get for the condition under study, which isn't matched with the meditation group for time and attention.