The Prevalence and Diagnosis of Depression in People with Mild or Borderline Intellectual Disability: Multiple Instrument Testing Tells Us More

ABSTRACT Introduction Estimates of the prevalence of depression in people with intellectual disability range from almost nonexistent to 39%. We analyzed the outcomes of three screening instruments to find out more about the prevalence in people with mild or borderline disability. Methods 102 Dutch individuals residing in institutions or living independently took part. The Beck Depression Inventory, the Glasgow Depression Scale and the Signaallijst Depressie voor Zwakzinnigen were used. Results Using the standard cutoff values, the numbers of people identified as depressed by the tests were 31%, 44%, and 22%, respectively. These were high numbers, and they did not refer to the same cases. When scoring above cutoff on all three tests simultaneously was the criterion, 13.7% of the participants were identified as depressed. Conclusion The combined use of several measuring instruments taught us that depression in people with intellectual disabilities might occur more frequently than often assumed: 13.7% might be the lower limit of its actual prevalence. People in this group still run the risk of being underdiagnosed.