Not really, it's still just a survey, and there is no way that any of them could be an expert of every effect (social, economical, crime, their relationships) o

Not really, it's still just a survey, and there is no way that any of them could be an expert of every effect (social, economical, crime, their relationships) of every drug. Without actual tests it was purely subjective. Change drug laws in a city for a period of time, heavily track the before and after effects, then repeat it in another city, and another city. That would be a study that would be more scientifically accurate.