Subdepartment of Clinical Health Psychology, University College London
West Berkshire Traumatic Stress Service
Royal Holloway, University of London
Brent, Kensington, Chelsea & Westminster Mental Health Trust, London
Camden & Islington Community Health Services NHS Trust, London
University of Pennsylvania, USA
Correspondence: Chris R. Brewin, Subdepartment of Clinical Health Psychology, University College London, Gower Street, London WC1E 6BT, UK
Declaration of interest The study was funded by the NHSE London Regional Office (project no. RDC01702). The views and opinions expressed herein do not necessarily reflect those of the NHSE (LRO) or the Department of Health.
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ABSTRACT |
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Aims To test and cross-validate a brief instrument that is simple to administer and score.
Method Forty-one survivors of a rail crash were administered a questionnaire, followed by a structured clinical interview 1 week later.
Results Excellent prediction of a PTSD diagnosis was provided by respondents endorsing at least six re-experiencing or arousal symptoms, in any combination. The findings were replicated on data from a previous study of 157 crime victims.
Conclusions Performance of the new measure was equivalent to agreement achieved between two full clinical interviews.
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INTRODUCTION |
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METHOD |
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Measures
Screening questionnaire. This was designed for trauma victims in
general and consisted initially of a single sheet of 16 items. Of these, five
were re-experiencing items and five were arousal items taken from the PTSD
Symptom ScaleSelf Report version (PSSSR;
Foa et al, 1993). As
in our previous work, the threshold for a positive response was designed to
correspond to a rating of 2 on the 0-3 scale employed by the original
PSSSR. The PSSSR instructions were amended as follows:
Please consider the following reactions which sometimes occur after a
traumatic event. This questionnaire is concerned with your personal reactions
to the traumatic event which happened to you. Please indicate whether or not
you have experienced any of the following at least twice in the past
week. Respondents ticked either Yes (scored 1) or
No (scored 0). A further three items enquired about negative
emotions and there were three filler items, but analyses involving these items
are not reported. The final 10-item version of the Trauma Screening
Questionnaire (TSQ) is given in the Appendix.
Clinician-Administered PTSD Scale (CAPSI; Blake et al, 1995). This is a well-validated structured clinical interview designed to elicit the frequency and severity of symptoms and to assign a DSMIV diagnosis. Interrater and testretest reliability are good (Blake et al, 1995). In this study a subsample of 28 CAPS interviews were subjected to independent blind rating, which produced 100% agreement on the presence or absence of a PTSD diagnosis with the interviewer rating.
Procedure
In the course of routine clinical follow-up following their involvement in
the train crash, teams from the Brent, Kensington, Chelsea & Westminster
Mental Health Trust and the Royal Berkshire Hospital contacted patients by
letter, inviting them to take part in a study of the care received following
major disasters. The 41 respondents agreeing to take part (18 out of 44
contacted from St Mary's; 15 out of 25 contacted from the Royal Berkshire
Hospital; no response data available from the survivors' group) were asked to
describe their current reactions to the accident and its aftermath by
completing the screening questionnaire. They then gave consent for a second
interview conducted approximately 1 week later, during which the CAPS was
administered. All interviews, which took place between May and November 2000,
were conducted by telephone and were tape-recorded. Patients meeting the
criteria for PTSD at the second interview were informed of their diagnostic
status and treatment options were discussed with them.
Analysis
The performance of the screening instrument was assessed by reference to
two standard criteria: sensitivity (i.e. the probability that someone with a
PTSD diagnosis will have tested positive) and specificity (i.e. the
probability that someone without a PTSD diagnosis will have tested negative).
These criteria are independent of the prevalence of the disorder in the
population, and so can be compared readily across studies. In practice, the
researcher or clinician generally wants to know the answer to two slightly
different questions that are sensitive to population prevalence. What is the
probability that someone with a positive test will report a diagnosis of PTSD?
What is the probability that someone with a negative test will not receive a
PTSD diagnosis? The answers to these questions are given by the positive and
negative predictive power of the screening test, respectively. The performance
of the test was also expressed in terms of the percentage of cases correctly
classified as having or not having PTSD (overall efficiency).
Sample 2: crime victims
Participants
We recruited victims of violent crime from police and hospital sources. The
157 participants who entered the study (118 men, 39 women) had an average age
of 35 years (s.d.=13 years). Full details of the sample are given in Rose
et al (1999).
Measures
Post-traumatic stress symptoms and diagnoses were assessed using the
PSSSR (Foa et al,
1993). As before, symptoms were counted as present if they were
rated at least 2 on the 0-3 scale. A diagnosis of PTSD was assigned if the
DSMIIIR criteria of at least one re-experiencing symptom, three
avoidance/numbing symptoms and two arousal symptoms were met. Diagnoses based
on the PSSSR have been shown to be highly concordant with diagnoses
based on structured interviews (Foa et
al, 1993).
Procedure
Participants completed the PSSSR during interviews that in all cases
were conducted within 1 month of the crime (mean 21 days post-crime, range
9-31 days, s.d.=5.6 days). Thus, participants did not fulfil the duration
criterion for a DSMIIIR diagnosis of PTSD, although they
fulfilled all other criteria.
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RESULTS |
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Performance at these two cut-offs is presented in Table 1, which shows that either of these thresholds offers overall efficiency of around 80%. Although both thresholds perform similarly, arguably the threshold of three re-experiencing symptoms offers the best balance of sensitivity and specificity. Using a threshold of four re-experiencing symptoms would improve specificity but at a cost of weaker sensitivity. A threshold of three arousal symptoms would again offer relatively more sensitivity, but the threshold of four arousal symptoms offers relatively better specificity and optimum overall efficiency. Table 1 also shows the diagnostic efficiency of requiring respondents to endorse at least six out of the ten re-experiencing or arousal symptoms in any combination. This cut-off maximised overall efficiency and led to a substantial increase in sensitivity and specificity, with excellent positive and negative predictive power.
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Sample 2: crime victims
Forty-two respondents received a PSSSR diagnosis of PTSD, which is a
prevalence rate of 26.8%. Performance at the cut-offs of three re-experiencing
symptoms and four arousal symptoms again maximised overall efficiency, which
ranged from 88% to 92% (Table
2). As with the rail crash survivors, we investigated what was the
optimum criterion for endorsing any combination of the ten re-experiencing and
arousal symptoms. Once again the optimum cut-off was six symptoms, yielding a
comparable level of overall efficiency and excellent positive and negative
predictive value.
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DISCUSSION |
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This is a striking result for a number of reasons. One reason is that with the rail crash survivors we were capitalising on post hoc analyses of the data designed to yield optimum prediction, whereas in re-analysing the crime victim data we were replicating previously established cut-off scores. The second reason is that with the crime victims the items used for prediction were also used in the calculation of PTSD, whereas among the rail crash survivors prediction was kept separate from the diagnosis of PTSD. Finally, the crime victims study utilised a questionnaire assessment of PTSD status, whereas with the rail crash survivors we used a structured clinical interview. Despite these promising findings, it will be important to establish the criterion validity of the instrument in other settings and with other traumas in order to overcome any possible sources of bias in the two samples used.
Comparison with existing instruments
Most existing instruments involve the use of rating scales and decision
rules, and contain 17 items or more (see
Brewin et al, 2002,
for a review). They can be scored in two ways, either requiring respondents to
meet the diagnostic criteria for PTSD (endorsing at least one re-experiencing
symptom, three avoidance/numbing symptoms and two arousal symptoms) or to
exceed a cut-off score. Data regarding the performance of such measures have
been published by Blanchard et al
(1996) using the PTSD
Checklist, by Foa et al
(1997) using the
Post-traumatic Diagnostic Scale, by Davidson et al
(1997) using the Davidson
Trauma Scale and by Bao
lu et al
(2001) using the Traumatic
Stress Symptom Checklist. The performance of briefer screening instruments has
been reported by Meltzer-Brody et al
(1999) using the 4-item SPAN,
and by Fullerton et al
(2000) using the BPTSD-12 and
BPTSD-6. However, the performance of some of these brief measures is probably
inflated by the use of post hoc cut-off scores and none has yet been
adequately validated. When we required the endorsement of at least six
re-experiencing or arousal items in any combination, the overall efficiency of
the screening instrument in this study was superior to all these measures, of
whatever length. Performance was equivalent to that obtained from a comparison
of diagnoses yielded by the two most highly regarded interview assessments
currently available for PTSD: the Structured Clinical Interview for DSM-IV
(SCID; First et al,
1996) PTSD module and the CAPS. In a sample of 123 combat
veterans, a CAPS total score of 65 was found to have a sensitivity of 0.84 and
a specificity of 0.95 relative to a SCID diagnosis
(Blake et al,
1995).
General considerations in screening for PTSD
It is quite possible that other combinations of symptoms would be as
effective as using the re-experiencing and arousal items. Previously it has
been claimed that the avoidance and numbing symptom cluster is likely to be
most efficient for screening purposes, because it is less common to reach the
threshold for these symptoms than it is for the re-experiencing and arousal
symptom clusters (e.g. North et
al, 1999). Our data show that the greater predictive power of
the avoidance and numbing cluster is almost certainly due to the fact that
more symptoms are required to meet the criterion. If equivalent numbers of
re-experiencing or arousal symptoms are required, levels of prediction appear
to be just as good. Avoidance and numbing symptoms were not included in our
instrument for several reasons. First, there are more of these items, so the
length of the instrument would be increased; second, some of the items (e.g.
the amnesia and foreshortened future items) are not always well comprehended
by respondents.
To be useful, screening instruments ideally should be short and contain the minimum number of items necessary for accurate case identification. They should be simple and preferably not require respondents to ponder over large numbers of alternative scale points. They should be written in a language that is easy to understand. Their purpose should be plain and they should be acceptable to respondents. For ease of administration, self-report questionnaires would appear to be the most flexible solution. If they are to be scored by non-specialists, which would widen their applicability, simple decision rules for determining who passes and fails the screen would be at a premium. Also highly desirable for successful instruments is that they be accurate at detecting both current PTSD and the risk of future PTSD, and that they should work well with different traumas, with different periods of time elapsed post-trauma and with varying prevalence of PTSD.
Our instrument appears to meet most of these criteria. All the items are simple and easy to understand. The use of a clear frequency threshold allied to a Yes/No response format also simplifies matters for respondents, whereas other measures require them to make ratings on four- or five-point scales. Moreover, having a single symptom scale makes our measure extremely practical for use by other health professionals, who may not be familiar with the disorder and with the structure of PTSD symptom clusters. We have shown that among crime and disaster victims excellent levels of prediction can be obtained with as few as ten items, and that enquiring about more PTSD symptoms has little additional value for screening purposes. It should be noted that all these data were collected, on average, 3 weeks post-trauma or later, and our experience is that screening usually should be delayed until this time, because during the initial post-trauma period natural recovery processes are in operation (Brewin, 2001). The next step is to implement the use of the instrument in primary health care or hospital settings in order to demonstrate that it is effective in improving the identification and treatment rates for cases of PTSD.
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Clinical Implications and Limitations |
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LIMITATIONS
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APPENDIX |
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REFERENCES |
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Received for publication July 5, 2001. Revision received January 2, 2002. Accepted for publication January 17, 2002.