Systematic Review of the Prevalence and Incidence of Intellectual Disabilities: Current Trends and Issues

TLDR: Heterogeneity in study settings, methodologies, age groups, and case definitions contributed to a range of prevalence estimates, and future research should include reproducible and consistent definitions of intellectual disabilities and monitor changes in prevalence over time.

Abstract: The prevalence of intellectual disabilities is often quoted at 1 %. A meta-analysis of articles published between 1980 and 2009 confirmed this prevalence. Changes in diagnostic practices, population characteristics, and exposure to known risk factors in recent years place this estimate in question and make it imperative to examine more recent studies of prevalence and incidence. Twenty relevant articles were obtained from five databases (PubMed, Embase, PsycInfo, Cochrane, and MEDLINE), published between 2010 and 2015. Most studies (n = 17) only reported prevalence estimates, while two provided incidence estimates. Various methodologies were applied, with the majority of studies (n = 16) using administrative data. Heterogeneity in study settings, methodologies, age groups, and case definitions contributed to a range of prevalence estimates (0.05 to 1.55 %). Future research should include reproducible and consistent definitions of intellectual disabilities, provide age-specific estimates, and monitor changes in prevalence over time.