[raldi]

I've read that it's notoriously difficult to measure the impact of crack on prenatal development because so many crack-smoking pregnant women also smoke cigarettes, and the latter is so harmful already that it's hard to isolate the effects of the former.

[clavalle]

That doesn't make a lot of sense since there are plenty of pregnant tobacco smokers that don't smoke crack.

[raldi]

I'm not following; could you elaborate?

[josephlord]

The control group should be smokers not non-smokers and if all the cocaine using group are also smokers the difference should be the effect of the cocaine.