Linking National Public Services Data to Estimate the Prevalence of Intellectual Disabilities in The Netherlands: Results from an Explorative Population-based Study

Objectives: Individuals with intellectual disabilities (ID) depend on public services for daily support and medical care; however, this group of individuals can be difficult to identify within population data. This therefore limits the opportunities to accurately estimate the size of the population with ID, monitor trends and tailor public health interventions according to the needs and characteristics of this group. By linking relevant databases, this study sought to identify individuals with ID in national data, to estimate the prevalence of ID based on public service use and to explore how this method can be used to better monitor the population with ID.

Study Design: Explorative data linkage study using the Dutch population register and databases from public services accessible with an ID diagnosis.

Methods: The overall prevalence of ID in the Dutch adult population was estimated, specified by age group and sex, and the identified ID groups were also characterised by their support needs. Participants included the entire adult Dutch population who were alive on 1 January 2015.

Results: After linking databases, 187,149 adults with ID were identified within a population of almost 12.7 million Dutch adults, giving an ID prevalence estimate of 1.45%. Prevalence of ID was higher among males (1.7%) than females (1.2%). Most individuals with ID were identified through the use of residential care services (n = 91,064; 0.7%). Non-residential ID-related care was used by 27,007 individuals (0.2%). Social, employment or income support due to a (mild) ID was received by 69,078 individuals (0.5%); the mean age in these ID groups was between 8 and 10 years which is younger than that in the general Dutch population. ID prevalence declined with increasing age across all ID subgroups.

Conclusions: The ID prevalence in The Netherlands, as determined by ID-related public service usage, aligns with international estimates. This suggests that national supportive services are accessible and used by individuals with ID. Moreover, this demonstrated that databases from national supportive services can be a useful resource to identify individuals with ID at the population level and can enable structural monitoring of the ID population through linking national databases.