Slate Star Codex has a really excellent blog post discussing the complex relationship between smoking and schizophrenia:
Schizophrenics smoke. A lot. Depending on the study, about 60-80% of schizophrenics smoke, compared to only about 20% of the general population. And they spend on average about 27% (!) of their income on cigarettes. Even allowing that schizophrenics don’t make much income, that’s a lot of money. Sure, schizophrenics are often poor and undereducated and have other risk factors for smoking – but even after you control for this, the effect is still pretty strong.
Various people have come up with various explanations. Cognitively-minded people say that schizophrenics smoke as a maladaptive coping strategy for the anxiety caused by their condition. Pharmacologically-minded people say that schizophrenics smoke because smoking accelerates the metabolism of antipsychotic drugs and so makes their side effects go away faster. Pragmatically-minded people say that schizophrenics smoke because they’re stuck in institutions with nothing to do all day. No points for guessing what the Freudians say.The full post has some great lessons for anyone involved in the business of identifying causal connections between variables--policymakers, scientists, social scientists, etc.
The example of smoking as a possible coping strategy for schizophrenics fits well within the broad trend in policy analysis towards appreciating more deeply the insights of individual behavior that might at first appear counterintuitive. The trend is best encapsulated in the book Poor Economics, but the idea is really just a refresh of approaches in lots of academic disciplines, from Hayek's theories about distributed knowledge to anthropology's 'culture as adaptation'.
We hear a lot these days about the myriad ways in which people make terrible decisions: in politics, diet, personal finance, etc etc. But it's helpful to occasionally reflect on the many good (or at least justified) decisions people make that baffle experts.