Diagnostic Overshadowing of Psychological Disorders in People With Intellectual Disability: A Systematic Review.

Diagnostic overshadowing is a bias in which symptoms of a psychological disorder are falsely attributed to a known diagnosis of intellectual disability. This systematic review evaluated all research on diagnostic overshadowing conducted to date, including dissertations and peer-reviewed journal articles. In total, 25 studies were included in this review. Findings suggest diagnostic overshadowing may not be as ubiquitous as originally believed, with one third of included studies finding no overshadowing. The quality of the evidence was graded as "Low" using the LEGEND tool, with common issues including outdated studies, analogue methodologies, small sample sizes and convenience samples, and inappropriate conducting or reporting of statistical analyses. Implications for the field and recommendations for future research are discussed.