Department of Psychology, University of Surrey, Guildford
Department of Psychology, Institute of Psychiatry, London
Department of Psychiatry, University of Oxford, UK
Correspondence: Professor Anke Ehlers, Department of Psychology, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK. Tel: 020 7848 5033; fax: 020 7848 0591; e-mail: a.ehlers{at}iop.kcl.ac.uk
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ABSTRACT |
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Aims To investigate prospectively the relationship between dissociative symptoms before, during and after a trauma and other psychological predictors, and chronic PTSD.
Method Two samples of 27 and 176 road traffic accident survivors were recruited. Patients were assessed shortly after the accident and followed at intervals over the next 6 months. Assessments included measures of dissociation, memory fragmentation, data-driven processing, rumination and PTSD symptoms.
Results All measures of dissociation, particularly persistent dissociation 4 weeks after the accident, predicted chronic PTSD severity at 6 months. Dissociative symptoms predicted subsequent PTSD over and above the other PTSD symptom clusters. Memory fragmentation and data-driven processing also predicted PTSD. Rumination about the accident was among the strongest predictors of subsequent PTSD symptoms.
Conclusions Persistent dissociation and rumination 4 weeks after trauma are more useful in identifying those patients who are likely to develop chronic PTSD than initial reactions.
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INTRODUCTION |
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However, the validity and utility of requiring dissociative symptoms as a core feature of ASD is controversial (Marshall et al, 1999). It remains unclear how the predictive power of dissociation compares with that of other early symptoms of PTSD in the aftermath of trauma, such as re-experiencing (Classen et al, 1998; Brewin et al, 1999), and with that of other established psychological predictors of PTSD, for example post-event rumination (Ehlers et al, 1998). Furthermore, dissociative symptoms are often transient (Spiegel & Cardena, 1990; World Health Organization, 1992). This raises the question of whether the persistence of dissociative symptoms beyond the traumatic event may be a stronger predictor of PTSD than initial reactions.
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METHOD |
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Out-patient sample
A consecutive series of 439 out-patients who attended the Accident &
Emergency Department of the John Radcliffe Hospital, Oxford, UK, following a
road traffic accident were invited to participate in the study and sent a
questionnaire package. A total of 176 patients (40%) opted into the study and
returned questionnaires. There were 79 female patients and 94 male patients
(on three questionnaires, gender was unidentifiable). The mean age of
respondents was 33.8 years (range 17-76, s.d.=13.3). Respondents were similar
to the total sample population sent questionnaires in terms of age and gender
distribution (58% male, mean age 32.2 years).
Measures
Symptoms of PTSD
Participants completed the Posttraumatic Diagnostic Scale (PDS;
Foa et al, 1997) at
initial and follow-up assessments. The PDS asks participants to rate how much
they were bothered by each of the PTSD symptoms specified in DSM-IV
(American Psychiatric Association,
1994), ranging from 0 (never) to 3 (5 times
per week or more/very severe/nearly always). The PDS yields a sum score
measuring the overall severity of PTSD symptoms. In addition, the
presence/absence of PTSD is determined by assessing whether a patient endorsed
the minimum number of symptoms required by DSM-IV for each of the symptom
clusters. We used the standard cut-off recommended by Foa et al
(1997) for determining the
presence of a symptom (at least 1=once a week/once in a
while).
Dissociation during the accident and persistent dissociation at 4
weeks
Dissociation during the accident and continued dissociation at 4 weeks were
assessed with the State Dissociation Questionnaire (SDQ). This is a seven-item
scale developed by the authors (further information available upon request),
measuring dissociative experiences such as de-realisation, de-personalisation,
detachment, altered time sense and reduction of awareness in surroundings. The
scale was developed in a series of studies with trauma survivors and student
volunteers and shows good reliability and validity
(Murray, 1997;
Halligan et al,
2002). The internal consistencies for the SDQ in the present
samples were Cronbach's factors of 0.75 (n=27) and 0.79
(n=173).
Pre-accident dissociative tendencies (trait dissociation)
Whether or not individuals dissociate during a traumatic event may depend
on individual personality differences in a general tendency to dissociate. The
Trait Dissociation Questionnaire (TDQ) developed by the authors (further
information available upon request) assessed the participants' pre-accident
disposition for dissociative experiences. The questionnaire contains 38 items
and was developed from a pool of 101 items taken from:
Murray (1997) described
data supporting the reliability and validity of the questionnaire. Factor
analyses indicated that the questionnaire measures seven different aspects of
dissociation, namely detachment from others and the world, sense of split
self, lability of mood and impulsivity, in-attention and memory lapses,
emotional numbing, confusion and altered sense of time and amnesia for
important life events. The internal consistency of the total score was
Cronbach's =0.93 (n=211) and the retest reliability over a
2-month period r=0.86 (n=83). Students with high scores on
the TDQ were more likely to experience intrusive memories of an unpleasant
videotape than those with low scores. The in-patient sample completed the full
TDQ and the out-patient sample completed a short 10-item version (TDQ-s). The
TDQ-s correlates highly with the TDQ (r=0.94,
n1=69 students, n2=27 in-patients). In
the present studies, the internal consistency for the TDQ in the in-patient
sample was Cronbach's
=0.92 (n=27) and the retest reliability
over a 6-month period r=0.82 (n=16). The internal
consistency for the TDQ-s in the out-patient sample was Cronbach's
=0.86 (n=176), and the retest reliability over a 6-month
period r=56 (n=129).
Memory fragmentation
Patients rated the degree to which their memory of the accident was
fragmented (Are your memories of the accident in any way unclear or
jumbled?) on a four-point scale from not at all to
a lot/very much. The in-patient sample also were asked to
provide a narrative of the accident. The interviewer (J.M.) rated these
narratives for the degree of fragmentation on a four-point scale
(0=very coherent, `=quite coherent, 2=not
very coherent, 4=very incoherent) without knowledge of
the patients' questionnaire scores.
Data-driven processing
Building on results from experimental cognitive psychology, Ehlers &
Clark (2000) suggested that
individuals who mainly engage in data-driven processing during trauma will be
more likely to show deficits in intentional recall of the trauma memory and to
suffer from subsequent re-experiencing symptoms than those who mainly engage
in conceptual processing. Patients in the out-patient study indicated the
extent to which they had engaged in data-driven processing (Were you
over-whelmed by different sensations and impressions?) and in
conceptual processing (Did you realise that you were in a dangerous
situation?) on a four-point scale from not at all to
a lot/very much. The data-driven processing score was the
difference between these two items.
Rumination
Rumination following the accident was assessed with the Rumination
Questionnaire (RQ). This is a six-item scale developed by the authors in a
series of studies (Murray,
1997; Clohessy & Ehlers,
1999; Steil & Ehlers,
2000; Halligan et al,
2002) assessing ruminative thoughts such as Do you go over
what happened again and again? and Do you dwell on what
happened, without really solving or deciding anything?. The internal
consistencies for the RQ in the present samples were Cronbach's =0.62
(n=27) and 0.77 (n=173).
Assessment of ASD
Patients were diagnosed as having ASD if they endorsed the minimum number
of symptoms specified in DSM-IV (American
Psychiatric Association, 1994) as assessed with the PDS and SDQ,
respectively, and if they met the disability criterion as measured by the PDS.
In addition to assessing whether or not patients met diagnostic criteria for
ASD in the 4 weeks after the accident, we assessed whether they met the
symptom criteria (but not the duration and disability criteria) for the
disorder at initial assessment.
Injury severity
For the in-patients and the first 86 participants of the out-patient study,
Abbreviated Injury Scores (AIS) were calculated from admission notes
(American Association for Automotive
Medicine, 1985). Out-patients also were asked to rate the degree
of their injuries on a four-point scale from not at all to
a lot/very much.
Procedure
In-patient sample
Patients were interviewed and they filled in the initial questionnaires in
hospital within 24 h of being admitted. Follow-up questionnaires were sent by
mail at 1, 2 and 4 weeks and 3 and 6 months after the accident. Owing to
incomplete return rates, a few of the 4-week data were estimated from the
2-week data (for participants with a PDS score of 0 at 2 weeks), yielding 21
participants for this assessment (78%). At the 6-month assessment, 21 patients
returned the questionnaires.
Out-patient sample
Questionnaires were sent out to patients within 48 h of the accident. The
vast majority of participants (82%) returned the questionnaires within the
first week of the accident. Follow-up questionnaires were sent at 4 weeks and
6 months after the accident. Return rates were 83% (n=146) at 4 weeks
and 80% (n=140) at 6 months.
Data analysis
Spearman correlation coefficients were calculated because the PDS scores
tended to be skewed to the left. For partial correlations and multiple
regression analyses, log-transformed PDS scores were used that normalised
distributions.
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RESULTS |
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Relationship of dissociation and other predictors with subsequent
PTSD symptoms
Table 2 shows the
relationships between the dissociation measures, the other cognitive
variables, injury severity and PTSD severity scores at 4 weeks and 6 months
after the accident.
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Dissociation measures
A pre-accident tendency to dissociate as well as dissociation during the
accident predicted the PTSD symptom severity. In the long term, however, the
dissociation variable that predicted chronic PTSD symptoms best was persistent
dissociation 4 weeks after the accident. Dissociation at 4 weeks predicted the
PTSD severity at 6 months over and above the initial dissociation (partial
correlations: rp=0.63 and P<0.01 for
in-patients; rp=0.47 and P<0.001 for
out-patients).
Further analyses tested whether the patients' reported pre-accident tendency to dissociate predicted dissociative responses during and after the accident. Dissociation during the accident showed moderate correlations with the patients' pre-accident tendency to dissociate (rs=0.53 and P<0.01 for in-patients; rs=0.33 and P<0.001 for out-patients). Partial correlations showed that, in the out-patient sample (but not in the smaller in-patient sample), dissociation during the accident continued to correlate with PTSD symptom severity at 4 weeks (rp=0.31, P<0.01) and 6 months (rp=0.19, P<0.05) when pre-accident tendency to dissociate was controlled. Partial correlations between persistent dissociation at 4 weeks and PTSD severity at 6 months, controlling for pre-accident tendency to dissociate, were significant in both samples (rp=0.51 and P<0.05 for in-patients; rp=0.47 and P<0.001 for out-patients).
We tested further whether the dissociation symptom cluster added to the prediction of PTSD symptom severity at 6 months over and above what could be predicted on the basis of the re-experiencing, avoidance and hyperarousal symptom clusters in the first 4 weeks after trauma, similar to an analysis of Brewin et al (1999). In a hierarchical regression analysis, we entered the presence/absence of the reliving, avoidance and hyperarousal cluster symptoms in the first step. These variables predicted 34% of the variance of PTSD severity at 6 months (R=0.58, R2=0.34, adjusted R2=0.32, F=20.98, d.f.=3, 124, P<0.0005). The dissociation symptom cluster significantly improved the prediction (R2 change=0.08, F change (1, 123)=16.97, P<0.0005) and the combination of all ASD symptom clusters, including dissociation, predicted 42% of the variance of PTSD symptom severity (R=0.65, R2=0.42, adjusted R2=0.40, F (4, 123)=22.00, P<0.0005). Similar results were obtained when PTSD severity at 4 weeks was predicted from symptom clusters at initial assessment, or when logistic regression analyses predicting the presence/absence of PTSD were used. The pattern of results did not change when a stricter cut-off of 2 was used for scoring symptoms on the PDS, as in the analysis of Brewin et al (1999).
Other cognitive predictors
Memory fragmentation tended to show a positive relationship with PTSD
severity. The expert rating appeared to be a better predictor than
self-reports of fragmentation. Memory fragmentation (self-reports) correlated
with both initial dissociation (rs=0.37,
P<0.001 for out-patients) and data-driven processing
(rs=0.27, P<0.001 for out-patients).
Data-driven processing during the accident correlated with PTSD symptoms. Partial correlations between data-driven processing and PTSD symptoms at both time points remained significant when dissociation during the accident was controlled for (4 weeks: rp=0.23, P<0.01; 6 months: rp=0.17, P<0.05).
Rumination about the accident was among the strongest predictors of PTSD. In the long term, the rumination variable that predicted chronic PTSD symptoms best was persistent rumination 4 weeks after the accident. It predicted PTSD symptoms at 6 months even when dissociative symptoms at 4 weeks were controlled for (in-patients: rp=0.56, P<0.05; out-patients: rp=0.42, P<0.001).
Multiple regression
How much of the variance of PTSD symptom severity 6 months after the
accident can be explained by dissociation and the other cognitive predictors?
In a hierarchical multiple regression analysis of the out-patient sample, the
variables taken at initial assessment were entered in the first step
(pre-accident dissociative tendencies, dissociation and data-driven processing
during the accident, initial memory fragmentation and rumination). These
variables explained 13% of the variance (R=0.36,
R2=0.13, adjusted R2=0.10, F
(5, 116)=3.54, P=0.005). In the second step, the variables taken 4
weeks after the accident were entered, that is, persistent dissociation,
memory fragmentation and rumination. These variables significantly increased
the accuracy of the prediction (R2 change=0.27, F
change (3, 113)=17.43, P<0.0005). Overall, dissociation and the
other cognitive predictors explained 41% of the variance of PTSD symptom
severity at 6 months (R=0.64, R2=0.41, adjusted
R2=0.37, F (8, 111)=9.69,
P<0.0005).
Injury severity
Injury severity as measured by the AIS was not a good predictor of
PTSD severity. However, the patients' own ratings of the severity of their
injuries correlated significantly with PTSD severity at 4 weeks and 6
months.
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DISCUSSION |
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ASD and PTSD
The prevalence rates of ASD and PTSD in the present samples have to be
interpreted with caution because they relied on a self-report questionnaire
rather than diagnostic interviews, and the appropriate cut-off for scoring
symptoms from such questionnaires is still under discussion
(Brewin et al, 1999).
However, our studies replicate earlier findings on the prevalence of ASD and
PTSD after road traffic accidents
(Blanchard et al,
1996; Ehlers et al,
1998; Harvey & Bryant,
1998), supporting the validity of the data. Previous studies have
shown that around 80% of patients who have ASD during the 4 weeks following
trauma will develop PTSD (Bryant &
Harvey, 1998; Harvey &
Bryant, 1998; Brewin et
al, 1999). The results of our out-patient study are
comparable but timing of assessment may be crucial. The ASD status may
fluctuate during the first 4 weeks following trauma and more persistent ASD
may be more predictive than initial ASD in predicting PTSD.
Dissociation as a predictor of PTSD
The present studies indicated that persistent dissociation is a stronger
predictor of chronic PTSD than dissociation during the accident. Persistent
dissociation at 4 weeks remained a significant predictor of PTSD severity at 6
months when pre-accident tendency to dissociate or initial dissociation was
partialled out. This pattern of results suggests that although initial
dissociation may put people at risk for PTSD, many are able to compensate by
post-event processing, or only those who continue to dissociate may be at high
risk of persistent problems.
The patients' reports of their pre-accident tendency to dissociate correlated with initial dissociation and subsequent PTSD symptoms. However, in line with the results of the retrospective study by Tichenor et al (1996), the prospective out-patient study found that dissociation during the accident predicted PTSD symptoms over and above a pre-accident tendency to dissociate. Thus, the contribution of a dissociative response to trauma on subsequent PTSD appears to be, in part, independent of pre-existing dissociative traits.
Overall, the studies supported the importance of dissociation in predicting PTSD. In contrast to the results of Brewin et al (1999) dissociative symptoms predicted later PTSD symptoms over and above what could be predicted from other PTSD symptoms, such as re-experiencing, avoidance and hyperarousal, even when the stricter cut-off for scoring the presence of PTSD symptoms used by Brewin et al (1999) was used. Further studies will have to clarify whether differences in the population studied or methodological differences may have contributed to the different results.
Other cognitive predictors
How does dissociation lead to later symptoms of PTSD? One possibility is
that dissociative symptoms are a sign of the individual's inability to process
fully the traumatic event and its implications
(Spiegel & Cardena, 1990;
van der Kolk & Fisler,
1995; Brewin et al,
1996; Foa & Hearst-Ikeda,
1996; Ehlers & Clark,
2000). Incomplete processing may lead to deficits in the memory of
the traumatic event, ranging from uncertainty about the sequence of events and
memory fragmentation to complete dissociative amnesia for the event. Such
deficits in trauma memory may be responsible for the easy triggering of
re-experiencing and hyperarousal symptoms characterising PTSD
(Brewin et al, 1996;
Foa & Hearst-Ikeda, 1996;
Ehlers & Clark, 2000). To
date, only preliminary evidence for this hypothesis is available. Amir et
al (1998) have reported
that fragmented trauma memories are indeed correlated with severity of PTSD,
and that the memories become more coherent with successful exposure treatment
(see Foa et al,
1995). Another study reported that survivors of road traffic
accidents with ASD gave more disorganised trauma narratives than those without
ASD (Harvey & Bryant, 1999).
The present studies are the first to provide prospective evidence for the role of memory fragmentation in PTSD. Patients' self-reports of memory fragmentation may be less reliable indicators of actual fragmentation than expert ratings, which tended to show a stronger relationship with subsequent PTSD. The present studies used global ratings, and more sophisticated measures may prove more of the trauma memory dysfunction. Halligan (1999) replicated the role of disorganised trauma memories in the development of PTSD following assault using a self-report questionnaire and several expert ratings. The authors also found a high interrater reliability of global experimenter ratings of memory fragmentation, such as the one used in the present study, supporting the validity of the present data.
The results of the out-patient study are in line with Ehlers & Clark's (2000) hypothesis on the role of data-driven processing during trauma. The significant correlations with memory fragmentation support the hypothesised link between this processing style and deficits in intentional recall of the trauma memory. As predicted, data-driven processing also predicted subsequent PTSD symptoms. The present study was the first to explore the role of this variable in a prospective study of PTSD, and a preliminary short measure of data-driven processing was used. It is therefore encouraging that Halligan (1999) could replicate the relationships between data-driven processing, memory fragmentation and subsequent PTSD symptoms in a prospective study of assault survivors.
The results on rumination extend earlier findings (Ehlers et al, 1998; Clohessy & Ehlers, 1999; Steil & Ehlers, 2000). Both initial and persistent rumination at 4 weeks were strong predictors of chronic PTSD. Rumination seems to be a maladaptive cognitive processing style that is quite independent of dissociation. Patients who ruminated excessively about questions such as why the trauma happened to them, how they could have prevented the trauma or its outcome or how they could get revenge for what happened to them were more likely to have chronic PTSD symptoms. At this stage, it is unclear what exactly the mechanisms are by which rumination maintains PTSD and in what ways it differs from helpful exposure to trauma memories. It may prevent patients from accepting that the trauma is an event from the past and may interfere with the formation of more complete trauma memories by focusing on what if questions rather than the experience of the trauma as it actually happened. It may also directly increase feelings of nervous tension, dysphoria or hopelessness, and cue intrusive memories of the event.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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REFERENCES |
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American Psychiatric Association (1994) Diagnostic and Statistical Manual of Mental Disorders (4th edn) (DSMIV). Washington, DC: APA.
Amir, N., Stafford J., Freshman, M. S., et al (1998) Relationship between trauma narratives and trauma pathology. Journal of Traumatic Stress, 11, 385-392.[Medline]
Bernstein, E. M. & Putnam, F.W. (1986) Development, reliability, and validity of a dissociation scale. Journal of Nervous and Mental Disease, 174, 727-735.[Medline]
Blanchard, E. B., Hickling, E. J., Barton, K. A., et al (1996) One-year prospective follow-up of motor vehicle accident victims. Behaviour Research and Therapy, 34, 775-786.[CrossRef][Medline]
Brewin, C. R., Dalgleish, T. & Joseph, S. (1996) A dual representation theory of post-traumatic stress disorder. Psychological Review, 103, 670-686.[CrossRef][Medline]
Brewin, C. R., Andrews, B., Rose, S., et al
(1999) Acute stress disorder and posttraumatic stress
disorder in victims of violent crime. American Journal of
Psychiatry, 156,
360-366.
Bryant, R. A. & Harvey, A. G. (1998)
Relationship between acute stress disorder and posttraumatic stress disorder
following mild traumatic brain injury. American Journal of
Psychiatry, 155,
625-629.
Classen, C., Koopman, C., Hales, R., et al
(1998) Acute stress disorder as a predictor of posttraumatic
stress symptoms. American Journal of Psychiatry,
155,
620-624.
Clohessy, S. & Ehlers, A. (1999) PTSD symptoms and coping in ambulance service workers. British Journal of Clinical Psychology, 38, 251-266.[Medline]
Ehlers, A., Mayou, R. A. & Bryant, B. (1998) Psychological predictors of chronic posttraumatic stress disorder after motor vehicle accidents. Journal of Abnormal Psychology, 107, 508-519.[CrossRef][Medline]
Ehlers, A. & Clark, D. M. (2000) A cognitive model of posttraumatic stress disorder. Behaviour Research and Therapy, 38, 319-345.[CrossRef][Medline]
Foa, E. B. & Riggs, D. S. (1993) Post-traumatic stress disorder in rape victims. In Annual Review of Psychiatry (eds J. M. Oldham, M. B. Riba & A. Tasman), Vol. 12, pp. 273-303. Washington, DC: American Psychiatric Association.
Foa, E. B., Molnar, C. & Cashman, L. (1995) Change in rape narratives during exposure therapy for posttraumatic stress disorder. Journal of Traumatic Stress, 8, 675-690.[Medline]
Foa, E. B. & Hearst-Ikeda, D. (1996) Emotional dissociation in response to trauma: an information-processing approach. In Handbook of Dissociation: Theoretical, Empirical, and Clinical Perspectives (eds L. K. Michelson & W. J. Ray), pp. 207-224. New York: Plenum Press.
Foa, E. B., Cashman, L., Jaycox, L., et al (1997) The validation of a self-report measure of posttraumatic stress disorder: the Posttraumatic Diagnostic Scale. Psychological Assessment, 9, 445-451.[CrossRef]
Halligan, S. L. (1999) Cognitive Processes Involved in the Maintenance of Post-Traumatic Stress Disorder. DPhil. Thesis, University of Oxford, Oxford, UK.
Halligan, S. L., Clark, D. M. & Ehlers, A. (2002) Cognitive processing, memory, and the development of PTSD symptoms: two experimental analogue studies. Journal of Behavior Therapy and Experimental Psychiatry, in press.
Harvey, A. G. & Bryant, R. A. (1998) The relationship between acute stress disorder and posttraumatic stress disorder: a prospective evaluation of motor vehicle accident survivors. Journal of Consulting and Clinical Psychology, 66, 507-512.[CrossRef][Medline]
Horowitz, M. J. (1976) Stress Response Syndromes. New York: Aronson.
Koopman, C., Classen, C. & Speigel, D. (1994) Predictors of posttraumatic stress symptoms among survivors of the Oakland/Berkeley, Calif., firestorm. American Journal of Psychiatry, 151, 888-894.[Abstract]
Marmar, C. R., Weiss, D. S., Schlenger, W. E., et al (1994) Peritraumatic dissociation and posttraumatic stress in male Vietnam theater veterans. American Journal of Psychiatry, 151, 902-907.[Abstract]
Marshall, R. D., Spitzer, R. & Liebowitz, M. R.
(1999) Review and critique of the new DSMIV diagnosis
of acute stress disorder. American Journal of
Psychiatry, 156,
1677-1685.
Murray, J. (1997) The Role of Dissociation in Posttraumatic Stress Disorder. DPhil Thesis, University of Oxford, Oxford, UK.
Sanders, S. (1986) The perceptual alteration scale: a scale measuring dissociation. American Journal of Clinical Hypnosis, 29, 95-102.[Medline]
Shalev, A., Peri, T., Canetti, L., et al (1996) Predictors of PTSD and injured trauma survivors: a prospective study. American Journal of Psychiatry, 153, 219-225.[Abstract]
Spiegel, D. & Cardena, E. (1990) Dissociative mechanisms in posttraumatic stress disorder. In Posttraumatic Stress Disorder: Etiology, Phenomenology, and Treatment (eds M. E. Wolf & A. D. Mosnaim), pp. 23-34. Washington: American Psychiatric Press.
Steil, R. & Ehlers, A. (2000) Dysfunctional meaning of posttraumatic intrusions in chronic PTSD. Behaviour Research and Therapy, 38, 537-558.[CrossRef][Medline]
Tichenor, V., Marmar, C. R., Weiss, D. S., et al (1996) The relationship of peritraumatic dissociation and posttraumatic stress: findings in female Vietnam theater veterans. Journal of Consulting and Clinical Psychology, 64, 1054-1059.[CrossRef][Medline]
Van der Kolk, B. A. & Fisler, R. (1995) Dissociation and the fragmentary nature of traumatic memories: overview and exploratory study. Journal of Traumatic Stress, 8, 505-525.[Medline]
World Health Organization (1992) The ICD-10 Classification of Mental and Behavioural Disorders: Clinical Descriptions and Diagnostic Guidelines. Geneva: WHO.
Received for publication June 8, 2001. Revision received December 3, 2001. Accepted for publication December 3, 2001.
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