> For starters, experimental bias isn't really an issue, here... This was an observational study, with crystal clear objective criteria for coding the dependent

> For starters, experimental bias isn't really an issue, here... This was an observational study, with crystal clear objective criteria for coding the dependent & independent variables. Just a nitpick: it was not an observational study, it was a true experiment, because they controlled the treatment: it was assigned by researchers at random. It is by definition not an observational study which have a distinctive feature that it doesn't control for a treatment.