A health professional might use an unstructured interview to elicit information from a patient about symptoms related to each of the diagnostic criteria for PTSD. He or she might also use a structured or semi-structured diagnostic interview such as the CAPS, SCID, PTSD Symptom Scale-Interview Version (PSS-I), the Structured Interview for PTSD (SIP), the DIS-IV, or the CIDI. The use of those instruments can inform professional judgment in a clinical setting, but they are more commonly used in epidemiologic and treatment outcomes research.

The CAPS is a semi-structured interview, developed by the Department of Veterans Affairs National Center for Post-Traumatic Stress Disorder. The CAPS should be administered by a trained health professional and can be used to determine whether a patient meets the DSM-IV diagnostic criteria for PTSD. It has the advantage of assessing the array of PTSD symptoms, as well as their severity (frequency and intensity), but it cannot be used to determine the presence of comorbid psychiatric disorders. The CAPS contains 34 questions, 17 of which measure symptom frequency and 17 measure symptom intensity. The CAPS generally takes at least 40 to 60 minutes to administer (Foa and Tolin 2000).

The SCID is a widely used structured clinical interview for psychiatric disorders that contains a PTSD-specific module with 19 items. Like the CAPS, the SCID-PTSD module has questions related to each of the DSM-IV diagnostic criteria; patients’ responses are listed as present, absent, or subthreshold. The SCID, like the CAPS, should be administered by a trained health professional. Unlike the CAPS, the SCID can be used to identify comorbid psychiatric disorders (Briere 2004); that is important because comorbid psychiatric disorders are common in PTSD patients. The SCID does not assess the severity of PTSD symptoms; the determination of whether a symptom passes a severity threshold is left to clinical judgment or further testing with a symptom-severity scale.