Sociological studies of the early 20th century can be regarded as predecessors of today's psychiatric epidemiology.[1]:6 These studies investigated for instance how suicide rates differ between Protestant and Catholic countries or how the risk of suffering from schizophrenia is increased in neighborhood characterized with high levels of social isolation. After World War 2 researchers began using community surveys to assess psychological problems.[1]:7 By the 1980s the development of new diagnostic assessment instruments and reliable criteria for mental disorders given by the DSM-3 began a trend to estimating the prevalence of mental disorders next to symptoms.
As an example, in an attempt to measure the prevalence of mental illness in the United States, Lee Robins and Darrel A. Regier conducted a study called the Epidemiological Catchment Area Project which surveyed samples of the general population at five sites across America. In the study, it was found that about a third of all Americans suffer from mental illness at some point in their lives. This statistic is often referred to as lifetime prevalence.
Today, epidemiological studies focus on the etiology of mental disorders, i.e. the identification and quantification of causes underlying psychiatric problems and their mechanisms, rather than mere estimation of prevalence.[1]:11 It is not ethically possible to experimentally expose study participants to stressors suspected to cause psychiatric disorders, thus epidemiological techniques are required to study the etiology. For this purpose longitudinal studies, which follow children and adults for a long period of time, often for many years, are particularly useful. These allow the study of naturally occurring exposures and how they affect changes in psychiatric symptoms. Two notable historical studies focusing on etiology are the Dunedin Multidisciplinary Health and Development Study and the Christchurch Health and Development Study.[2] These studies began in the 70's and studied the impact of perinatal problems, genetic variants, sexual abuse and other adverse exposures on psychological problems in childhood and later in adulthood.
Many different instruments are used to assess mental disorders in epidemiological studies depending on the age of the participants, available recourses and other considerations. Studies featuring adolescents and adults often use structured interviewing, a technique in which a series of questions is administered by interviewers to determine whether an individual is disordered or nondisordered. Alternatively, questionnaire are used, which can be administered more easily. In epidemiological studies featuring children, psychopathology is often assessed using parent report, however, multi-informant approaches, e.g. the simultaneous use of parent, teachers and self-report, is popular as well.[2]
Psychiatric disorders show substantial heritability according to twin studies. A meta-analysis of most twin-studies conducted found a combined heritability of 46% for psychiatric disorders.[3] Given the large contribution of genetic variants on psychiatric disorders, one major focus of psychiatric epidemiology is psychiatric genetics. A combination of family and molecular studies are used within psychiatric epidemiology to uncover the effects of genetics on mental health. Twin studies estimate the influences of all genetic variants and effects, but, due to relying purely on relatedness information, are limited in explaining the specific genetic mechanisms and architecture underlying psychiatric traits. Molecular studies confirm findings from family studies that genetic variants can partly explain the occurrence of psychological problems, e.g. by quantifying the total contribution of common genetic variants.[4][5] Furthermore an increasing number of specific genetic loci are being associated with psychiatric disorders in large genome-wide association studies.
