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Psychosomatic Medicine 64:345-352 (2002)
© 2002 American Psychosomatic Society

ORIGINAL ARTICLES

Critical Incident Exposure and Sleep Quality in Police Officers

Thomas C. Neylan, MD, Thomas J. Metzler, MA, Suzanne R. Best, PhD, Daniel S. Weiss, PhD, Jeffrey A. Fagan, PhD, Akiva Liberman, PhD, Cynthia Rogers, BA, Kumar Vedantham, MD, Alain Brunet, PhD, Tami L. Lipsey, BA and Charles R. Marmar, MD

From the Department of Psychiatry (T.C.N., T.J.M., S.R.B., D.S.W., C.R., K.V., A.B., T.L.L.), University of California, San Francisco; and Columbia University School of Public Health (J.A.F., K.L.), New York, NY.

Address reprint requests to: Dr. Thomas C. Neylan, PTSD Program, Psychiatry Service 116P, VA Medical Center, 4150 Clement St., San Francisco, CA 94121. Email: neylan{at}itsa.ucsf.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
OBJECTIVE: Police officers face many stressors that may negatively impact sleep quality. This study compares subjective sleep quality in police officers with that in control subjects not involved in police or emergency services. We examined the effects of critical incident exposure (trauma exposure) and routine (nontraumatic) work environment stressors on sleep quality after controlling for the effects of work shift schedule.

METHODS: Subjective sleep disturbances were measured by the Pittsburgh Sleep Quality Index in police officers (variable-shift workers, N = 551; stable day-shift workers, N = 182) and peer-nominated comparison subjects (variable-shift workers, N = 98; stable day-shift workers, N = 232). The main predictor variables were 1) duty-related critical incident exposure to on-line policing and 2) work environment stress related to routine administrative and organizational aspects of police work.

RESULTS: Police officers on both variable and stable day shifts reported significantly worse sleep quality and less average sleep time than the two corresponding control groups. Within police officers, cumulative critical incident exposure was associated with nightmares but only weakly associated with poor global sleep quality. In contrast, the stress from officers’ general work environment was strongly associated with poor global sleep quality. Sleep disturbances were strongly associated with posttraumatic stress symptoms and general psychopathology.

CONCLUSIONS: A large percentage of police officers report disturbances in subjective sleep quality. Although the life-threatening aspects of police work are related to nightmares, the routine stressors of police service seem to most affect global sleep quality in these subjects. These findings may have implications for health and occupational performance.

Key Words: stress • psychological • sleep disorders • stress disorders • posttraumatic

Abbreviations: CD = control subject, day shift;; CIHQ = Critical Incidents History Questionnaire;; CV = control subject, variable shift;; ES = effect size;; GSI = Global Severity Index;; MS-CV = Mississippi Scale for Civilian Posttraumatic Stress Disorder;; PD = police officer, day shift;; PSQI = Pittsburgh Sleep Quality Index;; PTSD = posttraumatic stress disorder;; PV = police officer, variable shift;; SCL-90-R = revised 90-item Symptom Checklist;; SF-12 = Medical Outcomes Study 12-item Short-Form Health Survey;; WEI = Work Environment Inventory.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
The role of work-related stress on physical health in police officers has long been of concern. Police officers have been reported to have increased rates of cardiovascular and gastrointestinal disorders, divorce rates twice the national average, and suicide rates three times the national average (1–3). One mediator of adverse health effects related to traumatic and nontraumatic duty-related stressors in police officers may be disturbed sleep. In community and clinic studies, insomnia has been associated with poor job performance, accidents, impaired physical well-being, and increased use of alcohol (4–7). Police officers face many stressors that may negatively affect sleep quality, including rotating work shifts and chronic exposure to both critical incident stressors as well as routine occupational and organizational stressors.

A few studies have focused specifically on the prevalence of sleep complaints in police officers. The main focus is on the adverse effect of rotating shifts on mood and health complaints (8, 9). The sleep-wake cycle, under the circadian control of endogenous regulators or oscillators, can be disrupted by a misalignment between biological rhythms and the external demands of police work (8–10). This gives rise to sleep-wake complaints, mood disturbance, decreased work performance, general physical malaise (11), and increased use of sedative-hypnotic drugs (12).

Police officers are exposed to many different types of stressors that may affect sleep quality and physical health. They are exposed to traumatic stressors, including physical injury, injuring others in the line of duty, and witnessing death or injuries to other officers and civilians. The impact of this high rate of exposure on emotional health has long been a significant public health concern. In addition, police officers are exposed to chronic nontraumatic stress arising from the demands of their work environment. For example, police officers face pressures from supervisors, attorneys, judges, media, and the public that can lead to stress-related symptoms such as insomnia. Thus, police officers are exposed to stressors that may affect multiple domains of sleep, such as sleep initiation, sleep maintenance, and nightmares.

This study compares subjective sleep quality in active-duty police officers with control subjects not involved in police or emergency services. We assess the separate and combined effects of police-related critical incident exposure (trauma exposure) and routine work environment stressors on different domains of sleep quality. We hypothesized that police officers would report more sleep disturbances than control subjects and that poor sleep quality would be related to both critical incident exposure and nontraumatic, routine work environment stressors.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
Subjects
Police officers (N = 747) were recruited from the police departments of New York, New York, and Oakland and San Jose, California, in a study aimed broadly at examining levels of PTSD symptoms as well as risk and resilience factors of symptom development, including cumulative critical incident exposure. Potential participants were selected by each department’s personnel section from departmental personnel rosters. A proportionally higher pool of minority and women officers was identified. In all other respects selection was random and no systematic strata were specified. The group of 747 participants is best described as a convenience sample. More details about the specific sample characteristics can be found elsewhere (13–15). The final survey sample includes approximately 29% female and 48% minority officers. Three hundred thirty-eight comparison subjects were identified and recruited using a peer nomination strategy. Police officers were asked to identify people "just like yourself, who live in your area, whose work does not involve police, emergency services, or security work, but who you think could be well suited to do police work in terms of abilities, interests, and values."

All subjects received a confidential invitation that included letters of support from both the police union representatives and management along with a federal certificate of confidentiality. Those agreeing to participate were sent an informed consent form and a self-report questionnaire booklet with a self-addressed return envelope. On receipt of the completed booklets, police officer participants were mailed a reimbursement fee of $100; control subjects received $75.

Police and control subjects were divided into two subgroups, those who worked variable work shifts and those who worked stable day shifts. The groups were defined by the shift work section of the Work Environment Inventory (13), which measures the effects of variable shift work on psychological and interpersonal functioning and physical health. This strategy yielded two subgroups of police officers (variable-shift workers, N = 551; stable day-shift workers, N = 182) and two corresponding groups of peer-nominated comparison subjects (variable-shift workers, N = 98; stable day-shift workers N = 232). The demographic characteristics of the study sample are presented in Table 1. Most subjects were in their late thirties, married, and had attended college. The peer nomination strategy produced a control sample that differed from the police officer samples in two respects; control subjects were more likely to be white and to have never been married. However, for the sample as a whole and within both police and control groups, separate analysis of variance tests for ethnicity and marital status on the dependent sleep variables did not show significant group effects.


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  		Table 1. Demographic Characteristics of Police Officers and Peer-Nominated Control Subjects
 
Measures
The dependent variables in this study are derived from the responses to the Pittsburgh Sleep Quality Index (PSQI) (16) and the items assessing nightmares on the Mississippi Scale for Civilian Posttraumatic Stress Disorder (MS-CV) (17). The PSQI is a 19-item self-report questionnaire, previously validated by polysomnography, that assesses sleep quality and disturbances that have occurred during the past month. The 19 individual items yield seven component scores: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. Scores on the seven dimensions are summed to form a single global score. A PSQI score of greater than 5 has been shown to have sensitivity of 89.6% and specificity of 86.5% ({kappa} = 0.75) for distinguishing good sleepers from subjects with clinical insomnia (16).

The assessment of nightmares as reported on the MS-CV was derived from the two items that refer to frightening dreams: "I have nightmares of experiences in my past that really happened," and "My dreams at night are so real that I awaken in a cold sweat and force myself to stay awake." The response format for these items is a 1 to 5 Likert scale ranging from low to high frequency.

The primary variables used to predict sleep disturbances were the total scores from the Critical Incident History Questionnaire (CIHQ) and the Work Environment Inventory (WEI). The CIHQ (18–20) provides a quantitative estimate of cumulative exposure to critical incidents. It is derived from a checklist of critical incidents potentially experienced in the domain of police work. The total score incorporates both frequency of exposure and a rating of coping difficulty for each item, summed across items.

The WEI was developed to assess routine work stress separate from critical incident stressor exposure in police officers (21). The scale includes items related to police-specific work stressors, such as court decisions and safety, as well as generic work stressors, discrimination, and shift work items.

The secondary variables used to predict sleep disturbances were general psychiatric and PTSD symptoms and nonduty-related trauma exposure. General psychiatric symptoms were assessed using the revised 90-item Symptom Checklist (SCL-90-R) (22). The SCL-90-R is a self-report measure for assessing 90 symptoms experienced during the past 7 days, rated on a five-point Likert scale ranging from 0 (not at all) to 4 (extremely). For the purpose of this study, the items related to disturbed sleep were not included. The global severity index (GSI) thus reflects the mean severity of all symptoms except the sleep items. Exposure to traumatic stress outside police duty was assessed with the Trauma History Questionnaire (23). Secondary analyses of the effect of shift work on waking function used the items rating fatigue in the SCL-90-R and energy level in the Medical Outcomes Study 12-item Short-Form Health Survey (SF-12) (24).

PTSD symptoms were assessed with the MS-CV (17). Subjects were instructed to select one duty-related critical incident that had to this day been "the most troublesome, disturbing, or distressing." This instrument was used to assess cumulative intrusive, avoidance, and hyperarousal responses since the time of the worst critical incident. The civilian version has been used to assess PTSD symptoms in nonveteran control subjects in the National Vietnam Veterans Readjustment Study (25) and in emergency services personnel after a disaster (26). The items related to disturbed sleep were removed.

Statistical Analysis
All analyses were two tailed, with the {alpha} level set at 0.05. Type I error was controlled using the false discovery rate procedure (27) for each family of tests. Our sample varies from the complete survey data set in that we excluded 14 police officers and 14 control subjects because of missing data for the main dependent variable (PSQI). This yielded 733 police officers and 330 control subjects. For these groups, the percentage of scattered missing data for the independent variables ranged from 3.0% to 4.6%. Data were found to be missing completely at random as determined by Little’s test (28) ({chi}2(76) = 88.3, p = .16). Missing values for the continuous independent variables were imputed using the expectation maximization method (29). An a priori power analysis indicated greater than 80% power to detect correlations of magnitude 0.10 and 0.15 in officers and control subjects, respectively.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
Variable-shift police officers had significantly higher mean PSQI global scores, indicating more disturbed sleep, than variable-shift control subjects (PSQI global scores: 6.1 vs. 5.1; ES = 0.32, t = 2.71, p = .007). Similarly, stable day-shift officers had significantly worse global sleep quality than stable day-shift control subject (PSQI global scores: 6.2 vs. 4.9; ES = 0.43, t = 4.18, p < .001). The frequency distributions of the PSQI global sleep quality score for the four groups are presented in Figures 1 and 2. Both groups of police officers reported significantly less time asleep than either of the two comparison groups. The mean total sleep time calculated from the PSQI was 378 minutes (SD = 80.9) for variable-shift police officers (PV), 371 minutes (SD = 69.3) for stable day-shift police officers (PD), 405 minutes (SD = 64.4) for variable-shift control subjects (CV), and 405 minutes (SD = 62.2) for stable day-shift control subjects (CD) (F = 11.52, p < .001, df 3, 1024; significant contrasts were PV, PD < CV, CD). The calculated mean sleep efficiencies for the four groups ranged from 91.1% to 92.6% with no significant differences between any of the groups. Prescription or nonprescription sleep medication was used a minimum of once a week in 12.2% of PV officers, 15.4% of PD officers , 10.2% of CV subjects, and 10.8% of CD subjects, which represented no significant differences across the four groups.



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  		Fig. 1. Frequency distribution of global PSQI score in police and control subjects who work variable shifts.

 


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  		Fig. 2. Frequency distribution of global PSQI score in police and control subjects who work a stable day shift.

 
Buysse et al. (16) found that a PSQI global score >=5 was the optimal cutoff score for distinguishing good sleepers from subjects with clinical insomnia. The percentage of respondents with PSQI global scores >=5 in our sample was as follows: 64.1% for PV officers, 63.7% for PD officers, 44.9% for CV subjects, and 50.4% for CD subjects. Using the higher cutoff score of 8 suggested by Carpenter and Andrykowski (30) to distinguish good from poor sleepers in treatment-seeking medically ill patients, the percentage of respondents with PSQI global scores in the clinical insomnia range was 29.9% for PV officers, 26.9% for PD officers, 19.4% for CV subjects, and 14.7% for CD subjects.

The effect of variable-shift vs. stable day-shift work on global sleep quality was not significant within either the police officer or control groups. We explored the effect of shift work on waking function by comparing fatigue (SCL-90-R) and energy level (SF-12) item scores in variable-shift vs. stable day-shift subjects. There were no differences in the mean rating for fatigue in variable-shift (mean = 1.1, SD = 1.0) compared with stable-shift police officers (mean = 1.2, SD = 1.0). However, variable-shift control subjects had a significantly higher mean score on the fatigue item (mean = 1.2, SD = 0.9) than stable day-shift control subjects (mean = 0.9, SD = 0.8; t(324) = 2.4, p = .015). There were no differences in reported energy level across the four groups.

The reports of trauma-related nightmares was low and not significantly different across the four groups. The MS-CV item assessing trauma-related nightmares was endorsed as "very true" or "extremely true" in 4.4% of police variable-shift workers, 5.0% of police stable day-shift workers, 7.4% of control variable-shift workers, and 5.8% of control stable day-shift workers. Although control subjects with stable day shifts reported significantly more dream-related awakenings than day-shift police officers (t = -2.95, p = .003), the frequency of this item in all the groups was low. The item assessing dream awakenings was endorsed as "very true" or "extremely true" in 1.8% of police variable-shift workers, 1.1% of police stable day-shift workers, 3.2% of control variable-shift workers, and 6.3% of control stable day-shift workers.

The variable-shift officers had higher CIHQ exposure scores than stable day-shift officers (mean = 18.8 (8.0) vs. mean = 17.0 (7.3); ES = 0.23, t = 2.74, p = .006). There were no significant differences in routine work environment (WEI) scores, Mississippi scale, or SCL-90-R scores between the two police officer groups.

The relationship of critical incident exposure, work environment stressors, age, gender, work shift, PTSD symptoms, and general psychopathology to different domains of sleep quality are presented in Table 2. The magnitude and direction of the relationship between the predictor and sleep variables did not differ between variable-shift and stable-shift police officers. Therefore, the correlation matrix in Table 2 presents the combined samples of police officers. Global sleep quality disturbances were weakly but significantly correlated with critical incident exposure as indexed by the CIHQ (r = .13, p < .01). The CIHQ was also significantly correlated with nightmares (r = .17, p < .01) and dream awakenings (r = .15, p < .01). There was a stronger relationship between global sleep quality and work environment stressors as indexed by the WEI (r = .31, p < .01). The WEI was also significantly associated with nightmares (r = .20, p < .01) and dream awakenings (r = .19, p < .01). Global sleep disturbances, nightmares, and dream awakenings were all strongly related to scores on the modified Mississippi PTSD scale and the modified SCl-90-R in which both predictor variables were modified to remove the sleep items. There was no significant effect of gender on sleep quality. Finally, there were weak effects for age and the related variable, years of service, on sleep duration such that older subjects with more years of police service had shorter sleep duration.


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  		Table 2. Correlation of Predictor Variables to Sleep Quality in All Police Officers (N = 727)
 
We explored whether police officers with a history of nonduty-related trauma exposure had greater reported sleep disturbance. We conducted separate comparisons of police officers with and without a history of exposure to the following nonduty-related traumatic events in the Trauma History Questionnaire: 1) being robbed, 2) experiencing the murder of a close friend or family member, 3) combat exposure, 4) sexual assault or abuse, and 5) physical assault or abuse. We found no significant differences in global sleep quality, nightmares, or dream awakenings in police subjects with a history of exposure to any of the above items.

A hierarchical linear regression model was developed to explain global sleep quality in police officers. In step 1 of this model, age, gender, and work shift account for 0.8% of the variance in global sleep quality (F(3,695) = 1.80, p = .15). In step 2, the addition of the CIHQ to the model accounted for 1.2% of incremental variance (F(1,694) = 8.27, p = .004). In step 3, entering the WEI accounted for an additional 9.5% of the variance (F(1,693) = 74.14, p < .001). In step 4, entering PTSD and general psychiatric symptoms from the modified SCL-90 and MS-CV scores accounted for an additional 15.8% of the variance (F(2, 691) = 75.22, p < .001). We ran the model again, reversing the order of steps 3 and 4. After accounting for MS-CV and SCL-90, the addition of the WEI at step 4 added 0.9% of the variance (F(1,691) = 8.60, p = .003).

A hierarchical logistical regression model was developed to explain the occurrence of nightmares in police officers. The item assessing nightmares was dichotomized to describe presence or absence of nightmares. In step 1 of this model, age, gender, and work shift account for 0.6% of the variance (Nagelkerke R2) in nightmares ({chi}2(3) = 2.90, p = .41). In step 2, the addition of the CIHQ to the model accounted for 7.1% of incremental variance ({chi}2(1) = 35.66, p < .001). In step 3, the addition of the WEI accounted for an additional 2.6% of the variance ({chi}2(1) = 13.76, p < .001). In step 4, entering the SCL-90 and MS-CV scores accounted for an additional 15.8% of the variance ({chi}2(2) = 88.33, p < .001). We also reran the model reversing the order of steps 3 and 4. The addition of the WEI after accounting for MS-CV and SCL-90 did not significantly account for any incremental variance.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 
A large percentage of police officers in our survey report disturbances in subjective sleep quality. The high prevalence of disturbed sleep in this study is not explained by the effect of rotating work shifts. This suggests that there are factors intrinsic to police work that contribute to poor sleep quality. Sleep disturbances are more strongly associated with routine work environment stressors than exposure to police duty-related traumatic stress. Despite the perception that the dangerous life-threatening aspects of police work may take its toll on psychological and physical health, it seems to be the routine stressors of police service that most affect global sleep quality in these subjects.

The stronger association of disturbed sleep quality with occupational stressors, as compared with critical incident exposure, is consistent with several other published studies. In one study, officers reported that several aspects of the police organization were more psychologically stressful than exposure to danger in the line of duty (31). Another study found that psychological distress was better correlated with items in the Police Stress Survey describing organizational stressors (32) than exposure to danger or violence (33). Liberman et al. (13), in a detailed report from this same study focused on the development of the WEI, reported that nontraumatic occupational stressors were strongly associated with general psychiatric symptoms. An important question arises, however, in light of our expected finding of high correlations between sleep disturbances and measures of PTSD and general psychiatric symptoms. Although it is possible that elevated psychopathology may predispose individuals to perceive more work-related stress, it is well known that an adverse work environment contributes to psychological distress. Hence the decision on whether to enter work environment stress before or after accounting for psychopathology in multivariate predictions of sleep disturbances reflects one’s hypothesis regarding the direction of causality between the two predictors. Even in the more conservative models, work environment stress remains a significant predictor of sleep quality above and beyond general psychopathology.

There have been a number of additional studies examining occupational stress exposure and sleep disturbance in the general population. Perceived stress has been found in multiple studies to correlate with both subjective and objective disturbances in sleep (34). Longitudinal data examining daily stress levels and sleep have shown that periods of high stress are associated with a 1-SD decline in sleep time (35). Stressful life events are also associated with the onset of chronic insomnia (36). Once established, insomnia is associated with diminished life satisfaction and poorer interpersonal relationships (36). Occupational stressors, as indexed by the WEI, bear some resemblance to the concept of "hassles," which in other studies has been found to be associated with both poor sleep (37) and adverse health outcomes (38, 39).

This study did not find a significant effect of shift work on sleep quality in either the police or control subjects. Furthermore, there were no significant effects on daytime fatigue or energy level in the two groups of officers. In contrast and as predicted, for the control subjects there was an increase in fatigue ratings in the variable-shift work compared with day-shift controls. These data are at variance with earlier studies that have shown more sleep disturbances and daytime fatigue in police officers (8, 9). One parsimonious explanation would be that the subjective ratings of sleep and fatigue lack the sensitivity to detect the effect of shift work. An alternative, though more speculative hypothesis, is that the recent increased awareness of this issue, as reflected by the availability of publications geared to police administrators and personnel (40, 41), has led to improved administrative practices on shift preferences and frequency of shift changes. Finally, it is possible that the poorer sleep quality in police officers as a group masks the effect of shift work that is discernible in the control sample as measured by the fatigue ratings.

This high rate of disturbed sleep in police officers has implications for their physical and emotional health. Subjective sleep quality has been found to be related to measures of immunocompetence (42–44). Stress-induced sleep disturbance is associated with abnormalities in interleukin-1 ß and ß-endorphin circadian rhythms (45) and elevated daytime sympathetic predominance of heart rate variability (46). Several studies have shown that the effects of psychological stress on immune function may be mediated by sleep disturbances (47, 48). Stress-related sleep disturbances are associated with poor psychomotor performance and elevated urinary catecholamines (49).

The weak relationship between traumatic stress exposure and insomnia found in the present study is consistent with data from two large studies of Vietnam veterans. The first study, a survey of 4042 monozygotic and dizygotic Vietnam era veteran twins, found that combat exposure was weakly associated with sleep onset and sleep maintenance insomnia (50). The second study examined sleep disturbances in 3016 veterans surveyed in the National Vietnam Veterans Readjustment Study and similarly found a weak correlation between combat exposure and sleep continuity disturbances (51). In contrast, three studies have found a strong correlation between trauma exposure and the frequency of nightmares (50–52). This is consistent with findings in studies of sleep and PTSD that have shown disturbances in rapid eye movement sleep (53–55). In the current study, the relationship between critical incident exposure and nightmares in police officers was significant but not strong, perhaps because of the low base rate occurrence of nightmares, which has been reported in other studies of civilians (56). Similar to the twin and Vietnam veteran studies cited above, trauma exposure was associated more with nightmares than insomnia.

There are several limitations of this study that are a consequence of its cross-sectional design and the lack of polysomnographic measures. Nevertheless, the results suggest a high prevalence of insomnia complaints in police officers, both absolutely and in relationship to peer-matched control subjects, that potentially has implications for their physical and psychological functioning. Many police departments have made critical incident debriefing available to officers exposed to duty-related traumatic stressors out of recognition that effective psychological treatment may improve the occupational performance and quality of life of its members. The results from this study suggest that psychological interventions that have an expanded focus on the negative effects of routine police work environment stressors theoretically have the potential to improve sleep quality and sleep-dependent physical and psychological functioning. The findings also suggest a role for sleep hygiene interventions to enhance occupational performance and both psychological and physical well-being of police officers.


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
REFERENCES
 
This work was supported by the National Institutes of Mental Health (RO1 to C.R.M. and J.A.F.; R29 to T.C.N.) and the Police Departments in Oakland and San Jose, California, and New York, New York. Additional support was provided by the General Clinical Research Center, Moffitt Hospital, University of California, San Francisco, with funds provided by the National Center for Research Resources, 5 MO1 RR-00079, U.S. Public Health Service.


   NOTES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
ACKNOWLEDGMENTS
 REFERENCES
 
Presented at the 15th Annual Meeting of the International Society for Traumatic Stress Studies, November 14–17, 1999, Miami, Florida.

Received for publication September 6, 2000.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 ACKNOWLEDGMENTS
 REFERENCES
 

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