Sir,

Intellectual disability (ID) is characterized by significant limitations in both intellectual functioning and adaptive behavior that begin before the age of 18 years.\[[@ref1]\] Prevalence of ID has been reported around 1-3% population in the world and of these mild, moderate, severe, and profound ID affects about 85%, 10%, 4%, and 2% of the population, respectively.\[[@ref1][@ref2][@ref3][@ref4]\] According to Harris\[[@ref5]\] and Maulik *et al*.\[[@ref2]\] studies, the highest prevalence is in low income countries (16.41/1000 population), whereas for middle- and high-income countries is around 15.94 and 9.21/1000 population, respectively. Furthermore, the prevalence of ID is more among child/adolescent population (18.30/1000) in comparison with an adult population (4.94/1000).

In this study, data were extracted from the Statistical Center of Iran.\[[@ref6]\] According to census results in 2011, the prevalence of ID is around 13/1000 population in Iran. In [Figure 1](#F1){ref-type="fig"}, the prevalence of ID is showed according to age and gender. In general, the prevalence of ID among men (5.3/1000) is more than women (3.5/1000), and it has the highest rate for adolescents and young people.

![Prevalence of intellectual disability according to age and gender in Iran (per 1000 population), x-axis: (%), y-axis: age group](JRMS-20-714-g001){#F1}

The results in comparison to other studies showed that the prevalence of ID in Iran is lower than global estimates significantly. Because of the different definitions of ID and data collection methods, rates are different in Iran as compared with other countries.\[[@ref7]\] The study reveals that there is an extensive conceptual and methodological gap in the census method and we should pay more attention to reduce the gap. The International Classification of Functioning disability and health (ICF) is a comprehensive population health measurement framework applied for the scientific standardization of data on health and disability worldwide. ICF makes it possible to collect those vital data in a consistent and internationally comparable manner.\[[@ref8][@ref9]\] In 1998, in order to reach a universally accepted conceptual framework to define and classify disability, World Health Organization (WHO) has developed an instrument entitled the WHO Disability Assessment Schedule (WHODAS 2.0) that provides a standardized method for measuring health and disability across cultures. WHODAS 2.0 has been developed specifically to reflect key features of the ICF.\[[@ref10]\] The instrument has been used in many countries and it should be valid in Iran for increasing data quality in surveys and censuses.\[[@ref11]\] In conclusion, using the conceptual framework of ICF in censuses and national health surveys is important and essential in Iran. ICF - based prevalence can provide comparable data at the national and global level for health and social policy development and monitoring, health and disability-related legislation, and service provision and development of disability research.

Financial support and sponsorship {#sec2-1}
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Nil.

Conflicts of interest {#sec2-2}
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There are no conflicts of interest.
