> Which means that the other less common drugs must be a lot more addictive to bring the number down to 70% There's a confounding variable: the difficulty of o

> Which means that the other less common drugs must be a lot more addictive to bring the number down to 70% There's a confounding variable: the difficulty of obtaining drugs vs alcohol. This causes a selection bias and means that a higher proportion of heroin users are addicts than otherwise would be. You can't necessarily deduce that heroin is more addictive from that (although there are other ways I'm sure).