What would be a good instrument for an epidemiologic study of mental disorders?

Answer 1

This would depend on your question, your population, and your budget! If you just want a quick snapshot of the prevalence of various mental disorders in the general population, you could do a cross-sectional study. This are cheap, quick, and can access a variety of people. Just make sure your sample size is large enough to achieve adequate power and that your study group is representative of whatever group you are drawing conclusions about. If you want to do something more specific, like study the educational achievements of a group of children with autism, you may need to do something like a cohort study! And, you may need a bigger budget :)