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Prevalence of intellectual disability: A meta-analysis of population-based studies

Posted Feb 23 2011 8:19pm

Autism prevalence gets a lot of discussion here and elsewhere on blogs. But what about other prevalence numbers? Say, for intellectual disability? This is important on its own in this discussion. Intellectual disability (ID) is more common amongst autistics than in the general population. In addition, it is worth noting that even with something like ID, prevalence values vary.

In general, the prevalence of ID is about 1%. Similar to autism prevalence. The prevalence of ID varies by country and by income, and by age.


Prevalence of intellectual disability: A meta-analysis of population-based studies

Abstract

Intellectual disability is an extremely stigmatizing condition and involves utilization of large public health resources, but most data about its burden is based on studies conducted in developed countries. The aim of this meta-analysis was to collate data from published literature and estimate the prevalence of intellectual disability across all such studies. The review includes studies published between 1980 and 2009, and includes data from populations that provided an overall estimate of the prevalence of intellectual disability. Meta-analysis was done using random effects to account for heterogeneity. Sub-group analyses were also done. The prevalence of intellectual disability across all 52 studies included in the meta-analysis was 10.37/1000 population. The estimates varied according to income group of the country of origin, the age-group of the study population, and study design. The highest rates were seen in countries from low- and middle income countries. Studies based on identification of cases by using psychological assessments or scales showed higher prevalence compared to those using standard diagnostic systems and disability instruments. Prevalence was higher among studies based on children/adolescents, compared to those on adults. Higher prevalence in low and middle income group countries is of concern given the limitations in available resources in such countries to manage intellectual disability. The importance of using standardized diagnostic systems to correctly estimate the burden is underlined. The public health and research implications of this meta-analysis have been discussed.
Research highlights

The prevalence of intellectual disability across the world is around 1%. The prevalence is almost two times more in low and middle income countries compared to high income countries. Highest prevalence was seen in child and adolescent population. Using standardized diagnostic instruments and disability measurements leads to lower estimates compared to simple psychological assessment tools even if confirmed by clinicians.

emphasis added.

As with autism prevalence, we need to look at these numbers in context: the culture of the country, the methods used, diagnostic criteria.

Whenever you hear someone say something like “One in 110 children born today will have autism” you are listening to someone who doesn’t really understand the “estimate” part of prevalence estimate.

  1. Tweets that mention Autism Blog - Prevalence of intellectual disability: A meta-analysis of population-based studies « Left Brain/Right Brain -- Topsy.com:
    [...] This post was mentioned on Twitter by Kev, Alltop Autism. Alltop Autism said: Prevalence of intellectual disability: A meta-analysis of population-based studies http://bit.ly/hl4Uaq [...]
  2. Shannon:
    "Whenever you hear someone say something like “One in 110 children born today will have autism” you are listening to someone who doesn’t really understand the “estimate” part of prevalence estimate." What do you mean by this comment? I thought the 1/110 was a pretty close estimate. Is it not that accurate? Count me in as one of those who do not understand the estimate” part of prevalence estimate. :)

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