The impact of proposed changes to ICD-11 on estimates of PTSD prevalence and comorbidity.

The World Health Organization's posttraumatic stress disorder (PTSD) work group has published a proposal for the forthcoming edition of the International Classification of Diseases (ICD-11) that would yield a very different diagnosis relative to DSM-5. This study examined the impact of the proposed ICD-11 changes on PTSD prevalence relative to the ICD-10 and DSM-5 definitions and also evaluated the extent to which these changes would accomplish the stated aim of reducing the comorbidity associated with PTSD. Diagnostic prevalence estimates were compared using a U.S. national community sample and two U.S. Department of Veterans Affairs clinical samples. The ICD-11 definition yielded prevalence estimates 10-30% lower than DSM-5 and 25% and 50% lower than ICD-10 with no reduction in the prevalence of common comorbidities. Findings suggest that by constraining the diagnosis to a narrower set of symptoms, the proposed ICD-11 criteria set would substantially reduce the number of individuals with the disorder. These findings raise doubt about the extent to which the ICD-11 proposal would achieve the aim of reducing comorbidity associated with PTSD and highlight the public health and policy implications of such a redefinition.