[mattkrause]

An RCT for this would literally be insane. "Sign up and we might abduct your kid on Thursdays from 7-9pm, as well as 8-10 weekends/year."

Please though, give the researchers some credit. Controlling for demographic factors is sort of the bare minimum for something like this--which they attempted to do by including two "social position" factors in the model.

They also included some factors relating to childhood (presumably pre-Scouts) mental health, which might also help address selection bias.