Posttraumatic Stress Diagnostic Scale

Devised by: Edna B. Foa, PhD

Type of instrument: The Posttraumatic Stress Diagnostic Scale (PDS) is a 49 item paper and pencil or on-line, self-report instrument that is designed to assist with the diagnosis of Post Traumatic Stress Disorder (PTSD). The PDS is based on the DSM-IV (American Psychiatric Association, 1994) diagnostic criteria for PTSD. The PDS takes 10-15 minutes to complete and 5 minutes to hand score (Axford, 1999).

This review only focused on the paper and pencil self-report version of the PDS.

Use of PDS: The PDS was developed to provide a brief self-report instrument to assist with the diagnosis of PTSD and it provides a means of quantifying the severity of PTSD symptoms. It is not intended to replace the structured diagnostic interview (Doll, 1999). The PDS has been validated on a clinical population aged 18 to 65 years. Nevertheless, clinical judgment may be used in deciding whether to use PDS on individuals falling outside this age range. However, the PDS is not designed to be administered to children as the DSM-IV (American Psychiatric Association, 1994) criteria for PTSD in children are not represented in the PDS. The PDS manual recommends that the PDS should be used with at least eighth-grade reading level ability.

The PDS generates judgments on whether the DSM-IV (American Psychiatric Association, 1994) six diagnostic criteria for PTSD have been met, the level of impairment and a symptoms severity score.

The PDS translates the DSM-IV’s technical language into more common used language suitable for adults clients (Doll, 1999).

In Part 1 of the PDS the respondents are asked to read through a list of traumatic events and to checkmark any event they have witnessed or experienced. This section of the instrument corresponds to criterion A of the DSM – IV for PTSD.

In Part 2 the subjects are asked which of the events they have checkmarked in part 1 that most bothers them, and to briefly describe the traumatic event. Item 15 in this part of the instrument ascertains the length of time that has passed since the event occurred. Items in this part of the instrument also corresponded to DSM-IV PTSD Criteria A where the subjects are asked to mark whether they or someone else were physically injured during the event, and whether they thought they or someone else’s life was in danger.

Part 3 corresponded to DSM-IV PTSD Criteria B through to Criteria D:

Item 22 ascertains whether recurrent and intrusive distressing recollections of the event are persistently re-experienced

Item 23 ascertains whether recurrent distressing dreams of the event are experienced.

Item 24 ascertains whether the respondent suddenly acts or feels as if the traumatic event were recurring.

Items 25 and 26 ascertain whether the respondent experiences intense psychological distress at exposure to events that resemble or symbolise an aspect of the traumatic event.

Items 27, 28, 29, 30, 31, 32, 33, ascertain whether the subject is experiencing persistent avoidance of stimuli associated with the traumatic event or numbing of general responsiveness.

Items 34, 35, 36, 37, and 38 ascertain whether the subject has experienced persistent symptoms of increased arousal that was not present before the trauma.

Items 39 and 40 ascertain the duration of the symptoms:

Acute: when symptoms have been present for less than three months

Chronic: when symptoms have lasted three months or longer

With delayed onset: when symptoms onset occurred at least six months after the traumatic event

Part 4 ascertains the level of impairment in functioning

Norms

The normative sample used 248 subjects ranging between the ages of 18 and 65. The subject had experienced, witnessed or been confronted with a traumatic event that had occurred at least one month before the PDS was administered. None of the normative samples were actively psychotic and all could read or write English well enough to complete the PDS. The subjects were recruited from a number of treatment and research centres that had a high PTSD patient population such as the Veterans Administration Hospital, anxiety and PTSD treatment clinics, women’s shelters and emergency/trauma centres. To broaden the subject base, non-treatment seeking populations and a greater variety of traumatic events were included such as those at fire stations, ambulance stations and residential rehabilitation centres. The subjects were obtained from five East Coast states and two Midwestern cities of the United States. Figures reported in the PDS’s manual indicate that low- and upper-income subjects were in the majority in the sample, and that those of minority groups, such as Hispanic Americans were under-represented.

Foa et al. (1993) used 46 female rape victims and 72 female non-sexual assault victims who were assessed monthly for three months. All subjects had been assaulted within two weeks of the initial assessment. Individuals were excluded from the study if they had a previous or current diagnosis of organic mental disorder, schizophrenia, or paranoid disorder as defined by the DSM-III-R (American Psychiatric Association, 1987). They were also excluded if they were illiterate in English or if a family member or a romantic partner had assaulted them.

Foa et al. (1993) used clinical structured interviews such as the Structured Clinical Interview for the DSM-II-R (SCID; Spitzer, Williams and Gibbon, 1987) and the Diagnostic Interview Schedule (DIS; Robins, Helzer, Croughan and Ratcliff, 1981) to assess the PTSD diagnoses. The Impact of Event scale (IES; Horowitz, Wilner and Alvarez, 1979) was used to assess the severity of post-traumatic reaction.

Coffey, Dansky, Falsetti, Saladin and Brady (1998) reported the following norms of PDS when PDS was used to screen for PTSD in a Substance Abuse Sample:

Patients admitted between 1993 and 1994 to an adult in-patient and out-patient chemical dependency treatment program at a tertiary care training hospital (N = 118) were screened for a history of trauma within one week following detoxification. The average age of the sample was 34 years (SD = 8.7); the age ranged from 18 to 70 years old and 57% of the participants were women. 58 % of the participants were Caucasian while the remaining participants were African-American.

Within one week following detoxification, participants were interviewed with the National Women’s Study (NWS) PTSD Module (Kilpatrick, Resnick, Saunders & Best, 1998). Participants were then given a brief self-reported demographic questionnaire, the PDS, the IES (Horowitz, Wilner and Alvarez, 1979) and Symptom Checklist-90-R (SCL-90-R;Saunders, Arata &Kilpatrick, 1990).

Reliability

The PDS’s manual reports the following reliability:

Cronbach’s Alpha: A Cronbach alpha of .92 is reported by the author for the 17 items used to calculate the symptom severity score. This indicated a high internal consistency.

Test-Retest Reliability: 10 to 22 days after the first administration of the PDS, it was readministered to a sample. 110 valid retests were collected, with an average interval between administrations of 16.1 days. The subjects were instructed to complete the PDS about the same traumatic incident as the first time. The test-retest reliability of PTSD diagnoses obtained from the PDS was assessed using Kappa—the author reports a kappa of .74, with 87.3% diagnostic agreement between the two administrations. This data provides good support for the internal consistency and stability of scores using the PDS.

Cronbach’s Alpha: Cronbach’s alpha was calculated on the PDS on the scores of 44 subjects who completed the instrument at the second assessment. Alpha =.91 for the total score of the PDS. The average items-total correlation for the PDS was .60 with a range of r (42) = .27, p < .10 to r (42) = .77, p < .001. Alpha coefficients for the symptom cluster subscales were as follows: re-experiencing .78, avoidance .80, and arousal .82.

Test-Retest Reliability: Test-retest reliability was evaluated using data collected at the third (9 –10 weeks after attack) and fourth assessment (12 – 14 weeks post assault). One-month test-retest reliability of the PDS was calculated using 29 subjects who completed the PDS at the third and fourth assessment. Test retest reliability of the overall severity score of the PDS was .74. The re-experiencing subscale of the PDS had a test-retest reliability of .66, p< .001. The reliability coefficient of the avoidance subscale was .56, p <.005, and test retest reliability of the arousal scale was .71.

Coffey et al. (1998) reported the following reliability on the PDS:

Internal Consistency reliability: Alpha = .97 was demonstrated for the total score. Alpha coefficients for the severity subscale was =.95. Alpha coefficients for the frequency subscales was .94.

Validity

Face Validity:

The PDS answer sheet and manual is clearly organised and has a professional appearance. The test items correspond to DSM-IV (American Psychiatric Association, 1994) diagnostic criteria for PTSD indicating high face validity.

Convergent Validity:

The PDS was examined by correlating the Symptom Severity Score with other scales that measure psychological constructs associated with PTSD.

Correlation between the PDS and the scales measuring associated constructs (N= 230) are as follows:

Beck Depression Inventory (BDI; Beck and Steer, 1987) = .79

State index of State-Trait Anxiety Inventory (STAI; Spielberger, 1983) =.73

Trait Index of State-Trait Anxiety Inventory (STAI; Spielberger, 1983) =.74

Impact of Event Scale (Horowitz, 1992) Intrusion index = .80

Impact of Event Scale (Horowitz, 1992) Avoidance index = .66

The relation between the PDS and the Impact of Event Scale (IES; Horowitz et al., 1979), Rape Aftermath Symptom test (RAST; Kilpatrick, 1988), State-Trait Anxiety Inventory (STAI; Spielberger, Gorsuch, and Lushene, 1970), and Beck Depression Inventory (BDI; Beck, Ward, Mendelsohn, Mock and Erbaugh, 1961) were assessed using Pearson correlation coefficients. All measures were administered at 5 to 6 weeks post assault and on the second assessment. A total of 44 subjects completed the PDS.

The PDS total score significantly correlated to all of the measures. RAST total [ r (42) = .81, p < .001], STAI trait [ r (42) = .56, p< .001], IES avoidance ( r (40) = .53, p < .001], and STAI state [r (41) = .52, p < .001]. Cluster scores from the PDS were also significantly related to all of the other self-reported measures of symptomatology.

The convergent validity of the PDS was examined by comparing diagnoses based on the PDS to PTSD diagnoses based on the SCID. The SCID was conducted approximately 3 months after the assault and the PDS was administered one week later. Thirty six subjects were assessed with both the SCID and PDS. The positive predictive power of the PDS was 100% and the negative predictive power was 82%. Overall the PDS correctly identified the PTSD status of 86% of the subjects. Thirteen subjects were diagnosed with PTSD based on the SCID. Eight of the 13 were also diagnosed with PTSD based on the PDS resulting in a sensitivity of 62%. The PDS correctly identified all twenty-six subjects who were not diagnosed with PTSD according to the SCID.

Convergent Validity:

Convergent Validity was assessed by examining the relationship between PDS, SCL-90-R PTSD scale and the IES. The PDS total score was significant correlated with the SCL-90-R PTSD scale, r (110) = .79, p < .001, IES Avoidance subscale r (119) = .57, p < .001, IES Intrusion subscale, r (116) = .69, p < .001, and IES total score, r (116) = .66, p < .001.

Concurrent validity:

Concurrent validity was assessed by examining the relationship between the PDS total score and the NWS PTSD Module. Using a modified PDS total score of 28 as a cut-off, the PDS was able to correctly classify 39 of 44 current PTSD positive patients for the sensitivity rate of 89%, a specificity rate of 65% and an overall correct classification rate of 74%.

Scoring Method

The PDS requires 5 minutes to score by hand.

A diagnosis of PTSD is only made if all the six DSM-IV criteria are endorsed. If one or more of the criteria is not met a diagnosis of PTSD is not made. When a particular criterion cannot be assessed because the client omitted too many items, the criterion is considered incomplete and this precludes a diagnosis of PTSD.

The Symptom Severity Score ranges from 0 to 51 which is obtained by adding up the response weights of the individual’s responses to items 22 to 38. Each item enquires on how often a particular PTSD symptom has bothered the subject in the past month. The weights are as listed below:

0 = not at all or only one time

1 = once a week or less/once in a while

2 = 2 to 4 times a week/ half the time

3 = 5 or more times a week/ almost always

The cut-offs for the symptoms severity rating categories are listed below:

< 10 mild

>11 and < 20 moderate

>21 and < 35 moderate to severe

>36 severe

The number of symptoms endorsed can range from 0 to 17. This is obtained by counting the number of symptoms the respondent endorsed with a response other then 0 for items 22 to 38.

Discussion

The PDS appears to be an effective and efficient method of screening for PTSD. However, when used as a clinical screening instrument it always needs to be used in conjunction with a complete and thorough diagnostic interview. The PDS is a self-report instrument, which does not incorporate any formal scales to detect faking and formal validity scales, therefore, it is susceptible to malingering.

Studies exploring the psychometric properties of the PDS point to some concerns, which could compromise its potential to be generalised to the wider population. The normative sample had a majority of low and upper income subjects and minority groups, such as Hispanic American, were under-represented. Additional validation research utilising a larger and wider demographic sample needs to be conducted to ensure that the normative sample adequately represents all types of population to which the test is going to be used.

Another potential problematic issue is the fact that there are no reversed questions on the PDS. This may lead to the tendency for over reporting symptoms which may result from a propensity to record a high number of ‘Yes’ answers. Reversal questions would also more likely compensate for malingerers.

References

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4^th ed.). Washington, DC: Author.

American Psychiatric Association. (1987). Diagnostic and statistical manual of mental disorders (3rd Rev. ed.). Washington, DC: Author.

Axford, S. N. (1999). Review of the Posttraumatic Stress Diagnostic Scale. In Plake, B.S. and Impara, J.C. (Eds.). The Supplement to the Thirteenth Mental Measurement Yearbook. (pp. 225 –226) Nebraska. The Buros Institute of Mental Measurements of The University of Nebraska.

Beck, A.T., and Steer, R.A. (1987). Beck Depression Inventory manual. San Antonio, TX: The Psychological Corporation.

Beck, A.T., Ward, C. H., Mendelsohn, M., Mock, J., and Erbaugh, J. (1961). An inventory for measuring depression. Arch. Gen. Psychiatry. 4. 561-571.

Coffey, S.F., Dansky, B.S., Falsetti, S.A., Saladin, M.E., and Brady, K.T. (1998). Screening for PTSD in a substance abuse sample: psychometric properties of a modified version of the PTSD symptom scale self-report. Journal of Traumatic Stress, 11,393-399.

Doll, B. (1999). Review of the Posttraumatic Stress Diagnostic Scale. In Plake, B.S. and Impara, J.C. (Eds.). The Supplement to the Thirteenth Mental Measurement Yearbook. The. (pp. 225 –226) Nebraska. The Buros Institute of Mental Measurements of The University of Nebraska.

Foa. E. B. (1995). Posttraumatic Stress Diagnostic Scale Manual. United States of America: National Computer Systems, Inc.

Foa. E. B., Riggs, D.S., Dancu, C. V., and Rothbaum, B. O. (1993). Reliability and validity of a brief instrument for assessing post-traumatic stress disorder. Journal of Traumatic Stress, 6,459-473.

Horowitz, M. (1992). Impact of Event Scale (revised). Department of Psychiatry and Langley Porter Psychiatric Institute, 401 Parnassus Ave., Box 0984, San Francisco, CA 94143-0984: Author.

Horowitz, M.J., Wilner, N., and Alvarez, W.(1979). Impact of vent scale: A measure of subjective distress. Psychosomatic Medivine.41. 207-218.

Kilpatrick, D. G.(1988). Rape aftermath symptom test. In Hersen, M., and Bellack, A.S. (eds.), Dictionary of Behavioral Assessment Techniques. Oxford: Pergamon Press.

Kilpatrick, D. G., Resnick, H.S., Saunders, B.E., and Best,C.L. (1989). The National Women’s Study PTSD Module. Unpublished instrument. Charleston, SC: National Crime Victims Research and Treatment Centre, Department of Psychology and Behavoral Sciences, Medical University of South Carolina.

Norris, F.H. and Ried, J.K. (1997). Standardized self-report measures of civilian trauma and posttraumatic stress disorder. In J.P. Wilson and T.M. Keane (Eds.) Assessing psychological trauma and PTSD. The Guilford Press: New York. ISBN: 1-57230-162-7.

Robins, L.N., Helzer, J.D., Croughan, J., and Ratcliff, K.S. (1981). The NIMH diagnostic interview schedule: Its history characteristics and validity. Arch. Gen. Psychiatr. 38. 381 389.

Saunders, B.E., Arata, C.M., and Kilpatrick, D.G. (1990). Development of a crime related posttraumatic stress disorder scale for women within the Symptom Checklist-90-Revised. Journal of Traumatic Stress, 3, 439-448.

Spielberger, C.D. (1983). Manual for the State-Trait Anxiety Inventory. Palo Alto, CA: Consulting Psychologists Press.

Spitzer, R.L., Williams, J.B.W., and Gibbon, M. (1987). Structured Clinical Interview for DSM-III-R (SCID), Biometrics Research Department, New York State Psychiatric Institute. New York.

Above written by: Ms Jenny Corran

Reviewed, edited and approved by: Dr. Grant J. Devilly