Designing experiments in this area is not my expertise, but my inclination would be "study premature babies with and without crack" You could also simply study premature babies in general, and then study why crack seems to cause more premature babies.
I imagine somebody who is actually in this field would not have much trouble designing experiments to study premature "crack babies". Premature babies are something they chose not to study, not something that cannot be studied.
I imagine somebody who is actually in this field would not have much trouble designing experiments to study premature "crack babies". Premature babies are something they chose not to study, not something that cannot be studied.