It is not precisely known how many people have intellectual and developmental
disabilities. Indeed, even very trustworthy sources of information report data that
appear inconsistent. Most dependable sources, e.g., The Arc of the US, the American
Association on Intellectual and Developmental Disabilities (AAIDD), etc., tend to agree
on a small range of percentages — roughly 1.5% to 2.5% — of the total general
population. The Bethesda Institute looks into the data on intellectual and developmental disability numbers and comes up with some surprising findings. Read more...