  Identifying the risk factors for mental illnesses is of significant public
health importance. Diagnosis, stigma associated with mental illnesses,
comorbidity, and complex etiologies, among others, make it very challenging to
study mental disorders. Genetic studies of mental illnesses date back at least
a century ago, beginning with descriptive studies based on Mendelian laws of
inheritance. A variety of study designs including twin studies, family studies,
linkage analysis, and more recently, genomewide association studies have been
employed to study the genetics of mental illnesses, or complex diseases in
general. In this paper, I will present the challenges and methods from a
statistical perspective and focus on genetic association studies.
