[cmrdporcupine]

what about kids who don't do _any_ group

[redcalx]

Consider this; if those kids that would normally avoid scouts/guide were now forced to go because their parents saw reports of this study, then the effects could very well be negative, in turn cancelling out or even reversing the reported overall beneficial effects.

[redcalx]

It looks like they weren't included in the study because the authors deemed that they were subject to selection bias (correctly in my view).

[cmrdporcupine]

1. Define mental health in terms of adherence to the mean. 2. Find a group where adherence to the mean is mandatory in order to continue in the group. 3. Success, the group makes you mentally healthy!