Re:CAPS vs PDS

Hi Sandra:

As you know, the CAPS is a clinician administered scale. It assess seperately the frequency and severity of each of the 17 PTSD symptoms on a 0-4 scale. Thus, the full range of the total score is from 0-136. It also has scales to assess things like guilt that are associated with PTSD but not a part of the formal diagnosis. Considerable research has been done on the CAPS and it's psychometrics are quite sound. Deriving a diagnosis from the CAPS can be simple or complex, depending on which scoring rule you use. There are at least three of them. These rules are known to very in terms of sensitivity and specificity.

The PDS technically refers to a self-report measure. The full PDS has the advantage of being a true diagnostic insrument in that it leads the respondent through all of the criteria, starting with Criteria A (the trauma), through the various symptom clusters, and finally to duration and interference. When the symptom items are administered by a clinician, it is technically called the PSS-I (PTSD Symptom Scale - Interview). The symptoms of PTSD are scored for combined frequency and severity on a 0-3 point scale, for a total score range between 0-51.

Advantages of the CAPS:
1. To date, it has been more widely used, so there is some advantage of being able to reference your results to that of other researchers. In particular, it seems to be the "gold standard" in medication studies.

2. Some people like that fequency and severity are assessed seperately. It allows you to note patterns such as a person having low frequency of certain symptoms, but when they occur they are terribly severe. Or, the symptoms occur frequently but are not terribly bothersome. This kind of information gets rolled into a single rating on the PDS/PSS-I. However...(there's always a however), empirically, the two scales are very highly correlated and for the most part, you end up summing the scales anyway. So, you spend twice the amount of time (because you have to ask seperate frequency and severity questions for each symptom) to get the same in formation.

Regarding the PDS/PSS-I, it also has sound psychometrics and has good convergent validity with the CAPS. As I noted above, it takes less time to administer. Also, if you get the full PDS, it provides a nice model for assessing Criterion A.

Neither measure was designed to assess the things that are thought to go along with "complex PTSD" or DESNOS. You would need to add additional measures to assess the specific things you are interested in. For example, if you are interested in dissociation, you'd want to include something like the Dissociation Experiences Scale (DES) or the Peritraumatic Dissocication Scale (I think that's what it's called).

The CAPS also has the advantage of being free to qualified researchers, as it was created by researchers working for the federal government. You would need to contact the National Center for PTSD at Bosten and inquire about getting a copy. Edna usually makes responds to requests for copies of the PSS-I to qualified researchers. The PDS, however, is copywrited and therefore costs money.

That's my two cents worth.

Replies:

Re:CAPS vs PDS, by Sandra Paulsen Inobe PhD, 04/29/03 Re:CAPS vs PDS, by Cahill, 04/30/03 Re:CAPS vs PDS, by Sandra Paulsen Inobe PhD, 05/01/03

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