Post-Traumatic Stress Diagnostic Scale (PDS)

The Post-traumatic Stress Diagnostic Scale (PDS) was developed and validated by Edna Foa 1 to provide a brief but reliable self-report measure of post-traumatic stress disorder (PTSD) for use in both clinical and research settings. The scale is intended to screen for the presence of PTSD in patients who have identified themselves as victims of a traumatic event or to assess symptom severity and functioning in patients already identified as suffering from PTSD. The test is self-administered and can usually be completed within 10–15 min and requires a reading age of ∼13 years. The pencil and paper and computerized scoring versions of the PDS are available from the test distributor 2. Test items mirror DSM IV criteria for PTSD and items are framed in accessible language. Questions relate to the frequency of distressing and intrusive thoughts, post-traumatic avoidance and hyperarousal. The PDS has 49 items. A short checklist identifies potentially traumatizing events experienced by the respondent. Respondents then indicate which of these events has troubled them most in the last month. Respondents then rate their response to this event at the time of its occurrence to determine whether the DSM IV stressor criteria are met (Criterion A1 ‘the person experienced, witnessed or was confronted with an event or events that involved actual or threatened death or serious injury, or a threat to the physical integrity of self or others’ and Criterion A2, ‘the person's response involves intense fear, helplessness, or horror’). Using a four-point scale, respondents then rate 17 items representing the cardinal symptoms of PTSD experienced in the past 30 days. Finally, respondents rate the level of impairment caused by their symptoms across nine areas of life functioning. A diagnosis of PTSD is made only when DSM IV criteria A to F are met. The PDS includes a symptoms severity score which ranges from 0 to 51 and this is obtained by adding up the individual's responses of selected items. The cut offs for symptom severity rating are 0 no rating, 1–10 mild, 11–20 moderate, 21–35 moderate to severe and >36 severe. The PDS has high face validity because items directly reflect the experience of PTSD with high internal consistency (coefficient alpha of 0.92). Test–retest reliability was also highly satisfactory for a diagnosis of PTSD over a 2- to 3-week period (kappa = 0.74). Test–retest using symptoms severity scores yielded a highly significant correlation (0.83). Analysis also revealed an 82% agreement between diagnosis using the PDS and the Structured Clinical Interview for DSM 3. The PDS does not incorporate any formal scales to detect faking or inconsistent responses. The scale was validated on samples aged 18–65. The PDS has been used in a wide range of clinical and research contexts with a high degree of confidence when use of a structured clinical interview is impractical. PDS has been used in prospective treatment studies helping establish a role for cognitive behavioural therapy in those with established PTSD 4. Recently, the PDS has been employed in diagnosing PTSD in the emergency services 5.