Posttraumatic Stress Disorder 525
ever, limitations of the ADIS-IV have been noted such as the failure to provide a total
score cutoff for caseness or to recommend whether symptom item endorsements in the
rare or mild range should count toward meeting diagnostic criteria (Litz, Miller, Ruef,
& McTeague, 2002). Thus the ADIS-IV may not be as strong in diagnosing PTSD as it
is with other anxiety disorders.
Clinician- Administered PTSD Scale
The Clinician- Administered PTSD Scale (CAPS) is the most widely used and best
researched of the diagnostic interview schedules for PTSD. Developed by the National
Center for PTSD (Blake et al., 1998), the CAPS is a structured interview that assesses
current and lifetime DSM-IV diagnostic status and symptom severity of PTSD and
ASD. It consists of a 17-item life event checklist that patients complete over their entire
life according to whether the event “happened to me,” “witnessed it,” “learned about
it,” “not sure,” or “doesn’t apply.” From items endorsed on the checklist, the clinician
selects up to three events that were the worst or most recent and then asks for a descrip-
tion of the event and the client’s emotional response to each event to determine exposure
to trauma (i.e., DSM-IV Criterion A1 and A2). This is followed by 17 questions on the
frequency and severity of each of the core DSM-IV symptoms of PTSD which are rated
on four-point Likert scales that can be summed to create a severity score for each symp-
tom category. Five additional questions determine the onset and duration of symptoms
(Criterion E), as well as subjective distress and social and occupational impairment
(Criterion F). Three global ratings are made on validity of the patient’s responses, over-
all severity of PTSD symptoms, and degree of symptom change or improvement in past
6 months. Finally, 5 additional questions may be administered to assess the associated
features of guilt over actions, survivor guilt, reduction in awareness, derealization, and
depersonalization.
It includes a summary sheet in which a subscale score is calculated for each criterion
and it is determined whether the patient meets current and lifetime diagnosis of PTSD.
A total severity score can be determined by summing over the 17 core symptoms and
interpreted with respect to five severity scores ranging from asymptomatic to extreme,
with a 15-point change indicating clinically significant change (Weathers, Keane, &
Davidson, 2001). Nine different scoring rules can be used to derive PTSD diagnoses
from the CAPS frequency and intensity scores and will yield different prevalence rates
of PTSD depending on whether they are relatively lenient or stringent (Weathers, Rus-
cio, & Keane, 1999). Administration of the complete CAPS takes approximately 1 hour
(Keane et al., 2007).
The CAPS has sound psychometric properties. Based on five samples of Vietnam
veterans, Weathers et al. (1999) found high interrater reliability for the three symptom
clusters (r’s = .86 to .91) and kappas of .89 and 1.00 for test– retest reliability for a
CAPS PTSD diagnosis (see Weathers et al., 2001, for discussion). The 17 symptom items
also had high internal consistency and close agreement with a SCID-based diagnosis of
PTSD (sensitivity = .91; specificity = .84, efficiency = .88, kappa = .75). Weathers et al.
(1999) also found that the CAPS total severity score correlated highly with self- report
symptom measures of PTSD (r’s = .77 to .94) and moderately with depression and anxi-
ety symptoms (see Weathers et al., 2001, for discussion). In their review of 10 years of
research on the CAPS, Weathers et al. (2001) concluded that the CAPS has high inter-