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Assessment and Diagnosis of Posttraumatic Stress Disorder: Page 2 of 4

Assessment and Diagnosis of Posttraumatic Stress Disorder: Page 2 of 4

The CAPS has been studied extensively and has excellent psychometric properties. It is the most widely used structured interview for PTSD and has proved useful for a variety of clinical and research assessment needs. The CAPS published version includes the interview booklet, an interviewer’s guide, and a technical manual. The main disadvantage of the CAPS is that it contains many more questions and therefore takes longer than other interviews to administer; it also requires additional training to become proficient in its administration and scoring. Finally, it yields 2 scores that need to be combined to yield an overall index of the intensity of the PTSD symptoms.

The PTSD Symptom Scale–Interview (PSS-I) is a structured interview developed by Foa and colleagues18 to assess DSM-III-R criteria for PTSD. It consists of 17 questions that correspond to the symptom criteria for PTSD. The current version, modified for DSM-IV, includes combined frequency and intensity ratings. The PSS-I yields a severity/frequency score for each of the 3 PTSD symptom clusters as well as a total PTSD severity score. It also yields a PTSD diagnosis, which is obtained by following a rationally derived scoring system whereby an item is counted as a symptom toward a diagnosis if it is rated as 1 or more.

The PSS-I has excellent psychometric properties.18 It has strong internal consistency, good test-retest re-liability, and excellent validity. Furthermore, it correlates strongly with several self-report measures of PTSD, depression, and anxiety.

In a recent report, the PSS-I generally compared favorably with the CAPS.19 The PSS-I took significantly less time to administer than did the CAPS. PSS-I is relatively brief and easy to administer; it yields a PTSD diagnosis as well as continuous severity scores for the 3 symptom clusters and the full syndrome. It includes only a single question for each symptom and offers instructions on how to follow up on ambiguous responses.

The Structured Interview for PTSD, developed to assess DSM-III and DSM-III-R criteria for PTSD, was modified in 1997 to correspond to DSM-IV criteria and relabeled as the SIP.20,21 The SIP consists of 19 items, including 17 items that correspond to DSM-IV diagnostic criteria for PTSD and 2 items that measure trauma-related guilt. Items are rated on a 5-point scale and those that are rated as moderate or higher are considered symptom endorsements. The SIP yields a continuous measure of PTSD symptom severity as well as a dichotomous DSM-IV PTSD diagnosis.

The SIP has excellent interrater reliability and diagnostic agreement.20 Good diagnostic utility against the SCID PTSD module was reported as well. For the revised version, in addition to excellent test-retest reliability and interrater reliability, moderate to strong correlations with self-report measures of PTSD have been reported, as had moderate correlations with measures of depression and anxiety.21 Furthermore, the SIP has shown good sensitivity to clinical change as a treatment outcome measure.


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