This meta analysis collated data from published literature between 1980 and 2009 to estimate the prevalence of intellectual disability across all such studies.

The authors state the prevalence of intellectual disability across all 52 studies included was 10.37/1000 population. Estimates varied according to income group of country of origin, age-group of study population  and study design.

The authors found prevalence higher among studies based on children/adolescents, compared to those on adults and higher prevalence was also found in low and middle income group countries.

Prevalence of intellectual disability: A meta-analysis of population-based studies, Maulik P et al,  in Research in Developmental Disabilities, 32. 2. 419-436