Effects of varying scoring rules of the Clinician-Administered PTSD Scale (CAPS) for the diagnosis of post-traumatic stress disorder in motor vehicle accident victims.

We examined the effects of varying the scoring rules for the CAPS (Clinician Administered PTSD Scale) on the diagnosis of PTSD in a sample of 100 victims of recent motor vehicle accidents. This was done by assessing, for each scoring rule, the rate of categorical diagnosis and the effect on group mean scores on measures of subjective distress and role impairment. Changing from the most liberal to the most conservative scoring rule results in a change in diagnosis of PTSD from 44% to 29% of the sample. Comparisons of those included as PTSD under the most conservative scoring criteria vs those excluded (who had previously been included) reveal significantly greater subjective distress and role impairment among those who continue to be included in the PTSD category. Thus, changes in scoring rules have clinically significant effects on the incidence and severity of diagnosed PTSD. This indicates that the selection of scoring rules has important implications for epidemiological estimates of the prevalence of PTSD, and that PTSD studies using different scoring rules as inclusion criteria may be using somewhat different samples.