“…Although statistics are kept at the national or regional level in several European Union member states, the lack of standardization of definitions and in recruiting and including cases, 5 makes cross-country comparison of prevalence difficult, and the data may be of little use for planning, monitoring, and evaluation of national and regional policies. 6 Furthermore, the overall prevalence of intellectual disability is around 1% in Europe, but that of severe intellectual disability (including the moderate severe and profound categories, but excluding mild intellectual disability) is only 0.4%, 7 making the number of children in the latter group within one database insufficient for studying specific subgroup characteristics, examples of which include males born with a low birth weight, 8 the proportion of children with epilepsy frequenting mainstream school, and issues of aetiology 9,10 and social class distribution. 11 Different definitions, classifications, and ascertainment methods for intellectual disability that exist across the world continue to challenge the field of epidemiology.…”