History and Epidemiology of Intellectual Disability

The chapter outlines the history of intellectual disability over the centuries and highlights some of the key legislations, policies and scientific understanding that have evolved over the past centuries, which have also influenced the different diagnostic systems. The section on epidemiology gives a broad overview of some factors that determine the epidemiology of the condition, keeping in perspective the incidence, prevalence and mortality estimates; aetiology; and knowledge about health services research. The gaps in knowledge and future research are discussed.