A 2010 meta-analysis by an international team of mental health experts found that the worldwide prevalence of intellectual disability (ID) or mental retardation was around one percent. But the share of individuals with such a condition in low- to middle-income countries were up to twice as high as their wealthier counterparts because they lacked the sources needed to tackle the problem, such as preventing children from being born with ID due to hereditary conditions with antenatal genetic screening, poor child and maternal care facilities, and inadequate nutrition, leading to, for instance, iodine deficiency. The researchers also found that ID was more common among children and adolescents than adults. A 2020 literature review and meta-analysis confirmed that the incidence of ID was indeed more common than estimates from the early 2000s.