title: Population and sample: a major problem in psychiatric research.
mesh_terms: D002986:Clinical Trials as Topic; D006801:Humans; D001523:Mental Disorders / Q000453:epidemiology*; D010919:Placebos; D011379:Prognosis; D011570:Psychiatry; D011600:Psychopharmacology; D012106:Research; D012494:Sampling Studies; D013223:Statistics as Topic
chemical_list: D010919:Placebos