The Journal of Nervous & Mental Disease
© Williams & Wilkins 1997. All Rights Reserved. Volume 185(8), August 1997, pp 498-506
Risk Factors for Posttraumatic Stress Symptomatology in Police Officers: A Prospective Analysis


1 Department of Psychiatry, Academic Medical Center, University of Amsterdam, Tafelbergweg 25, 1105 BC Amsterdam, The Netherlands.
Send reprint requests to Dr. Carlier.
This study was supported by grants from the Dutch police forces, the Prevention Fund, and the General Civil Pension Fund.




This study examines internal and external risk factors for posttraumatic stress symptoms in 262 traumatized police officers. Results show that 7% of the entire sample had PTSD, as established by means of a structured interview; 34% had posttraumatic stress symptoms or subthreshold PTSD. Trauma severity was the only predictor of posttraumatic stress symptoms identified at both 3 and 12 months posttrauma. At 3 months posttrauma, symptomatology was further predicted by introversion, difficulty in expressing feelings, emotional exhaustion at time of trauma, insufficient time allowed by employer for coming to terms with the trauma, dissatisfaction with organizational support, and insecure job future. At 12 months posttrauma, posttraumatic stress symptoms were further predicted by lack of hobbies, acute hyperarousal, subsequent traumatic events, job dissatisfaction, brooding over work, and lack of social interaction support in the private sphere. Implications of the findings regarding organizational risk factors are discussed in the light of possible occupational health interventions.

Not every traumatized individual will develop posttraumatic stress disorder (PTSD; APA, 1987). The risks of doing so can be connected to the trauma itself, to preexisting vulnerability factors, or to an interplay between the two (Davidson and Fairbank, 1993). Predisposing vulnerability factors can include genetic susceptibility to general psychopathology or to specific psychological disorders, early adverse or traumatic experiences, personality characteristics such as neuroticism and introversion, recent life stress or life change, deficient support systems, recent heavy use of alcohol, external locus of control, and a pervasive sense of the uncontrollability of stressful events (Davidson and Foa, 1993, p. 229). The epidemiological literature is quite informative on this subject (Breslau et al., 1991, 1995; Helzer et al., 1987; Kessler et al., 1995). Apart from community-based studies, research on risk factors for PTSD has focused mostly on disaster victims (Green et al., 1990; Shore et al., 1986a, b), on Vietnam veterans (Card, 1987; Goldberg et al., 1990; Kulka et al., 1990; Snow et al., 1988), or on crime victims (Kilpatrick and Resnick, 1993).

Emergency service personnel constitute one group who are at risk of developing psychological problems from exposure to traumatic stressors (Carlier and Gersons, 1994; Gersons and Carlier, 1992, 1994). A few studies have concentrated on risk factors for emergency personnel. McFarlane's (1988a) findings, for instance, indicated that poor general adjustment, a history of past adversity, previous personal psychiatric problems or a family history of them, and a tendency to avoid thinking about the event in question were all predictive of symptomatic sequelae in a large group of fire fighters. A study by Bartone et al. (1989) of military health aid workers indicated that the level of exposure to the traumatic stressor is related to subsequent distress. A study by Weiss et al. (1995) showed dissociative tendencies to be strongly predictive of symptomatic response in emergency personnel. Marmar et al. (1996) found that those emergency services personnel who were suffering greater distress reported a greater degree of exposure, greater peritraumatic emotional distress, greater peritraumatic dissociation, greater perceived threat, and less preparedness for the critical incident.

One group of personnel who may be involved in emergency work is the police, who, like other emergency workers, are not immune to developing PTSD when they are exposed to an intense traumatic event (Doctor et al., 1994; Gersons, 1989). Although police officers are not usually called on to carry out emergency work at major disaster sites, their job does involve exposure to a wide range of emotionally distressing incidents, and police work is often cited as one of the most stressful occupations (Alexander and Wells, 1991; Duckworth, 1986; Hetherington, 1993). Empirically, traumatic police stressors can be divided into two categories: very violent incidents, implying active participation in events; and very depressing incidents, implying confrontation with consequences of events (Carlier and Gersons, 1992; Larsson et al., 1988). Examples of the former are shooting incidents, hostage-takings, or escalating riot situations; examples of the latter are confrontation with seriously injured victims or corpses and disaster rescue work. We consider the police as unique in that they regularly have to deal with both trauma categories in the course of their work. Most other rescue workers (for instance, fire fighters, paramedics, and emergency medical technicians) are confronted exclusively with very depressing incidents. Although there are other trauma-sensitive professional groups (for instance, public transportation employees, prison workers, or army personnel) who can face both violent and depressing events, they may not be on such a frequent scale as the police.

This study focuses on traumatized police officers, and it includes both categories of events, violent and depressing. No disaster work is included, as it did not occur around the time of the study. A number of internal and external risk factors for posttraumatic stress symptoms in police officers were examined.

Subjects and Procedure^

The research was part of the Dutch longitudinal research project known as Critical Incidents in Police Work. The total research group consisted of 262 Dutch police officers, 218 of them men and 44 women. The policemen's mean age (± SD) was 33 ± 5.7 years, ranging from 23 to 54 years; that of the police-women was 28 ± 3.5 years and ranged from 22 to 39. This study was designed to compare a group of 69 traumatized police officers exhibiting posttraumatic stress symptoms with a control group of 193 traumatized police officers without such symptomatology. The focus was on possible risk factors for posttraumatic stress symptoms.

In Table 1, background characteristics are shown for the two groups and for the entire sample. None of the differences between the two subgroups in Table 1 were statistically significant (p <.05). Variables concerning rank, income, race, and education (not in Table) were likewise equivalent across the subgroups. This indicates that the subgroups are appropriate replicates of one another.

TABLE 1 Comparison between Background Characteristics of Total Sample and Those of Officers with and without Posttraumatic Stress Symptomatologya,b

All the police officers participated voluntarily. After providing the participants with a full description of the study, we obtained their written consent. The study was approved by the Medical Ethics Committee of the Amsterdam Academic Medical Center. During the course of the study, participants were not undergoing any treatment.

Before the study, police personnel from five of the largest police departments in the Netherlands were informed by the authors about the purpose and the procedure of the study. They were told they could start participation whenever they had experienced a critical incident in their work. A list of 37 critical police incidents (categories depressing versus violent; see Carlier and Gersons, 1992) that could potentially cause PTSD was given to the departments. Officers who experienced an incident not included in the list (e.g., a divorce or labor dispute) were excluded. That critical incident that induced participation by an officer was taken as basis for the assessments (see below).


Measurements were taken 2 weeks after the critical police incident (baseline interview), after 3 months, and finally 12 months after the incident. All assessments for all participants consisted of a face-to-face interview with one of three independent assessors, lasting approximately 90 minutes. The assessors were trained research psychologists (R.L., W.E., M.S.). Nonparametric (chi-square) tests were performed to detect any researcher effects; none were found. The interviews were conducted in small, comfortable rooms at the police departments. The assessors took extensive notes during the interviews, and these were scored by an independent rater (I.C.). Interrater agreement concerning posttraumatic stress symptoms was.98.

The baseline assessment (after 2 weeks) with the baseline self-report questionnaire elicited information about the hypothesized risk factors for posttraumatic stress symptoms. (A detailed list with definitions of hypothesized risk factors can be obtained from the first author.) The perceived private support was measured with a Dutch equivalent of the Interpersonal Support Evaluation List (Cohen and Hoberman, 1983). The items about perceived support at work and about occupational stress were measured in accordance with the model of Caplan et al. (1980). Life events were measured according to the inventory compiled by Green (1993). Coping style was measured with a Dutch equivalent of the Ways of Coping Checklist (Folkham and Lazarus, 1980). Neuroticism and introversion were defined in conformity with Eysenck (1957), and these factors were measured with a Dutch equivalent of the Maudsley Personality Inventory (Jensen, 1958). Thrill- and adventure-seeking and boredom-susceptibility were measured according to the concept of Zuckerman (1979). The questions about trauma variables were developed especially for this study: mortal danger, duration, confrontation with injured persons or corpses, emotional exhaustion, number of critical incidents, severity, own injuries, and type of police trauma (depressing or violent). Other hypothesized risk factors we considered were civil status, age, education, gender, marital status, ethnicity, years of police experience, religion, rank, work absence due to illness, hobbies, previous psychiatric history, previous physical health history, and family history of physical or psychiatric problems. Correlations among the hypothesized risk variables were low to moderate.

PTSD diagnosis 3 and 12 months posttrauma was established by means of a structured interview for PTSD (SI-PTSD; Davidson et al., 1989). For the purpose of this study, we translated the interview and adapted it to DSM-III-R criteria (the study had begun before the introduction of DSM-IV). The SI-PTSD is designed not only to elicit information about the presence or absence of symptoms but also to scale how severely they are experienced, in both a current and a lifetime perspective. It also permits distinguishing between symptoms linked to the trauma under consideration and those related to some other trauma. In a recent review of available PTSD interviews, Blake et al. (1995) have concluded that the SI-PTSD has good reliability and validity. Concurrent validity with respect to the diagnosis of PTSD by the SCID has also been demonstrated (Davidson et al., 1989; Spitzer et al, 1990). The SI-PTSD used in this study rates each of the 17 DSM-III-R items (and one DSM-III item, guilt feelings) on a scale of 0 to 4, where 0 is absence, 1 is minimal/mild, 2 is moderate, 3 is severe, and 4 is extremely severe. A minimum score of 2 on a particular item was required for it to be regarded as present in a diagnostic sense.

Data Analyses^

Since there were not enough participants with full-blown PTSD (see Results section), any subsequent analysis of groups necessarily involves the dichotomizing of participants according to posttraumatic stress symptoms and no posttraumatic stress symptoms. In posttraumatic stress symptoms, we include subclinical levels of PTSD or partial PTSD. This condition is present when subjects exhibit fewer than 6 symptoms or fewer than 3 symptom groups needed to qualify for the PTSD diagnosis (Carlier and Gersons, 1995; Weiss et al., 1992).

The statistical analysis of risk factors for posttraumatic stress symptoms was done in two phases (Hosmer and Lemeshow, 1989). First, univariate analysis (likelihood ratio chi-square) was performed to select potential risk factors. Second, multiple logistic regression was applied to examine the effects of each risk factor, controlling for all other factors. Multiple logistic regression also enables us to study the statistical interaction between predictors of posttraumatic stress symptoms. Only those factors that were statistically significant in the first phase were included in the second. Besides the significance level of p <.05, we also examined p <.10 to identify possible trends in risk factors (Hauff and Vaglum, 1994).


Over the entire sample, we determined that 7% of the respondents had PTSD. For 6%, it was manifested 3 months posttrauma, whereas 1% had developed it between then and 12 months posttrauma. One respondent with PTSD also had a history of major depression and currently had dysthymia; two respondents with PTSD also met the criteria for personality disorder. Some 34% of the respondents exhibited posttraumatic stress symptoms or subthreshold PTSD at some time during the study (10% at 3 and 12 months; 18% at 3 months only; 6% at 12 months only).

The first phase of our risk analysis consisted of univariate analyses of all the hypothesized risk factors. We tested the mean differences between the groups with and without posttraumatic stress symptomatology. At 3 months posttrauma, the group with posttraumatic stress symptoms was found to score significantly higher on the hypothesized predictors emotional exhaustion at time of trauma, trauma severity, insufficient time allowed by employer to resolve the trauma, and insecure job future (respectively t = 7.54, t = 6.27, t = 2.11, and t = 3.21; df = 260, p <.05). Of the predictors at 12 months posttrauma, the posttraumatic stress symptomatology group scored significantly higher on trauma severity, job dissatisfaction, and brooding over work (respectively t = 4.79, t = 3.05, and t = 2.88; df = 260, p <.01).

We next compared the scores of our two subgroups with the normative samples as published in the manual. For the no posttraumatic stress symptomatology group, the mean score for introversion was lower than that of the normative sample (which had a range of 49 to 57; Wilde, 1970). The mean scores for insecure job future and for job dissatisfaction were also lower than the norm (mean = 2.4 ±.8; mean = 1.8 ±.9; Caplan et al., 1980). This means that this group's members were not introverted, perceived a good job future, and were satisfied with their jobs. Also, for the posttraumatic stress symptomatology group, the mean score for introversion was lower than the normative sample (range between 49 and 57) reported in the manual (Wilde, 1970), and the mean score for insecure job future was also lower (mean = 2,4 ±.8) reported in the manual (Caplan et al., 1980). This means that this group was not introverted and was sanguine about job future.

At 3 months posttrauma, significant correlations with both emotional exhaustion during trauma and trauma severity can be observed for all PTSD variables: intrusion, avoidance, hyperarousal subscales, and PTSD diagnosis. The variable insufficient resolution time correlated with PTSD diagnosis. Dissatisfaction with organizational support correlated with the avoidance subscale. Finally, the variable insecure job future correlated with the intrusion and hyperarousal subscales and with PTSD diagnosis.

At 12 months posttrauma, trauma severity still correlated significantly with all PTSD variables. Job dissatisfaction correlated with PTSD diagnosis. The variable brooding over work was correlated both with the hyperarousal subscale and with PTSD diagnosis. Lack of social companionship correlated with the avoidance subscale. For all significant correlations (p <.05), the higher the score on the scale in question, the more posttraumatic stress symptoms that were present. (A table showing the means and standard deviations for all variables, and the correlations of the predictors with the measurements of PTSD variables, can be obtained from the first author). Because the predictors mentioned were to an extent intercorrelated, we applied multiple logistic regression to clarify their relative contributions as well as the interactive influence of the predictors on posttraumatic stress symptoms. In logistic regression, the predictive value of each predictor is expressed in its so-called odds ratio, a measure of increased risk. Generally speaking, the higher a predictor's odds ratio, the greater a person's chance of developing posttraumatic stress symptoms when that predictor is present (Hosmer and Lemeshow, 1989).

In Table 2, we show the significant odds ratios for posttraumatic stress symptoms at 3 months and 12 months posttrauma in association with significant risk factors. At 3 months posttrauma, the odds ratios indicate that officers who were emotionally exhausted when the trauma occurred were 2.26 times more susceptible to developing posttraumatic stress symptoms than those not experiencing exhaustion. Another finding was that officers who have trouble expressing their emotions were 2.17 times more vulnerable than others (p <.10). The other variables listed in Table 2-introversion; trauma severity (p <.10); insufficient resolution time; dissatisfaction with organizational support; and insecure job future-each increase the risk of posttraumatic stress symptoms by a factor of approximately 1.5.

TABLE 2 Logistic Regression of Significant Risk Variables for Posttraumatic Stress Symptomatology 3 Months and 12 Months Posttrauma (N = 262).

At 12 months posttrauma, police officers without hobbies proved 2.87 times more vulnerable than colleagues with a hobby. The other predictors in Table 2 also contributed significantly to the development of chronic posttraumatic stress symptoms, but their impact was weaker. It can further be seen that the acute posttraumatic stress symptoms at 3 months posttrauma had considerable predictive value for posttraumatic stress symptoms at 12 months. Each of the symptoms, difficulty concentrating, sleep disturbance, intense distress from reminders of the trauma, and guilt feelings, was, as seen in their very high odds ratios, a strong predictor of posttraumatic stress symptoms 9 months hence. Generally, officers with acute hyperarousal symptoms were found to be 2.38 times more susceptible to chronic posttraumatic stress symptoms.


This study found that 7% of the total sample of police officers had PTSD, as determined by means of a structured interview. To begin with, we can compare this current PTSD rate with those in other populations (Marmar et al., 1996). Breslau et al. (1991) reported a lifetime PTSD prevalence rate of 9% in a sample of 1007 young adults from a Detroit health maintenance organization. Schlenger et al. (1992) reported a current PTSD prevalence rate of 15% among male Vietnam combat veterans. Norris (1992) found a current PTSD rate of 8% for subjects with diverse traumatic exposures. Resnick et al. (1993) found a current PTSD prevalence rate of 10% for female crime victims. Kessler et al. (1995) reported a lifetime PTSD prevalence rate of 8% in a subsample of the National Comorbidity Survey. Our finding of 7% current PTSD for the police more or less corresponds to the current PTSD prevalence rates for trauma victims in general and for crime victims. Prevalence rates for emergency services personnel have also been shown to be similar or slightly higher. For instance, in a study by Marmar et al. (1996), 9% of emergency services personnel were characterized as having symptom levels typical of psychiatric outpatients. Durham et al. (1985) reported that 10% of rescue workers developed significant distress 5 months posttrauma. One exception was the study by (McFarlane (1988b), who found PTSD rates of up to 30% in fire fighters. However, these higher rates of distress may reflect the volunteer status of the Australian fire fighters studied, as well as differences in disaster-related experiences (Bryant and Harvey, 1996; Marmar et al., 1996). The Marmar study (1996) is important in that it was able to compare different groups of emergency services personnel, including police, fire fighters, paramedics/emergency medical technicians, and road construction and maintenance personnel. An interesting finding here was that the police and fire groups had significantly lower distress levels than the other groups. This is in line with the relatively lower rate of PTSD for police in our study. Several reasons for these lower distress levels can be proposed. Police and fire personnel undergo preemployment psychological screening, which is designed in part to select persons who will be resilient to repeated stressors (Marmar et al., 1996, p. 81). Self-selection could also be a factor. That is, police and fire fighters who cannot cope may tend to pull out of these professions at an early stage. Further, police and fire personnel are specially trained for rescue operations and for handling acute stress situations (Marmar et al., 1996, p. 80).

It is interesting to note that PTSD in our study was not related to the type of police trauma (depressing or violent) that had been experienced. Green (1993) and March (1993) have proposed that severity of trauma and threat are probably more important predictors of posttraumatic stress than the type of stressor. This study indeed confirmed severity of trauma as a predictor of posttraumatic stress symptoms at both 3 and 12 months posttrauma.

At 3 months posttrauma, symptomatology in police officers was further predicted by introversion and by difficulty in expressing feelings and in addition by emotional exhaustion at the time of the trauma, insufficient time granted by one's employer for dealing with the trauma, dissatisfaction with organizational support, and insecure job future. At 12 months' posttrauma, symptomatology in police officers was predicted further by absence of hobbies, subsequent traumatic events, dissatisfaction with work, brooding over work, and lack of social interaction support in the private sphere. It thus appears from our findings that certain risk factors gain in importance when it comes to chronic PTSD. Other risk factors, by contrast, appear more instrumental in the development of posttraumatic morbidity (McFarlane, 1989).

Still other risk factors examined here, namely civil status, gender, age, rank, police experience, previous psychiatric problems, adverse life events before the trauma, posttrauma life events, or familial psychiatric illness, were found to bear no relation to posttraumatic stress symptoms. The fact that in this study gender was not related to posttraumatic stress symptomatology is inconsistent with the findings of Breslau et al. (1995) and Kessler et al. (1995) but consistent with those of Helzer et al. (1987), Davidson et al. (1991), Smith and North (1988), and Steinglass and Gerrity (1990). The results on civil status in this study are inconsistent with those of Kessler et al. (1995), who found that lifetime PTSD was significantly more prevalent among respondents who were married. Generally, results concerning the effects of marital status in studies of particular traumas are inconsistent (Card, 1987; Kulka et al, 1990; Solomon et al., 1987).

Some of the risk factors that we have found to be linked to posttraumatic stress symptoms have been confirmed by other researchers in relation to emergency personnel. For example, the risk factor introversion was also found by McFarlane (1989). In a study by Fullerton et al. (1992), social support was found to be particularly likely to mitigate the impact of rescue work in fire fighters. Emotional or mental exhaustion at the time of the trauma was also identified by Manor et al. (1995). Future research could assess the relation between emotional exhaustion at the time of the trauma and, for instance, peritraumatic dissociation (Marmar et al., 1994). Bryant and Harvey (1996) also found posttraumatic stress in volunteer fire fighters to be associated with multiple and recent incidents. Our own finding that acute hyperarousal symptoms were predictors of continued posttraumatic stress symptoms at 12 months posttrauma may seem somewhat at odds with those of McFarlane (1989) and Shalev et al. (1996). He found that a tendency to avoid thinking about the event was predictive of the fire fighters whose complaints took a more chronic course. Yet McFarlane (1992) later argued that avoidance appears to be a defense strategy to the distress generated by reexperiencing the trauma, rather than a primary link to the symptoms. Further support for this hypothesis can be found in the study by Helzer et al. (1987). They argued that symptoms indicative of hyperarousal and sleep disturbance were more characteristic of PTSD than were reexperiencing and emotional numbing (Helzer et al., 1987; McFarlane, 1992). This is consistent with our own findings as presented here.

Some of the other risk factors we found have not been previously investigated and therefore need further study. Those risk factors that relate to organizational characteristics could have significant practical implications for the prevention of posttraumatic stress symptomatology in emergency personnel. Factors such as dissatisfaction with work indicate that occupational stressors can render police officers more vulnerable to developing PTSD. Weiman (1977, p. 119) had earlier noted that job stress can affect a worker's psychosocial and physiological homeostasis. We would furthermore like to stress that insufficient time allowed by the employer to resolve the trauma is a major organizational risk factor. A police organization could easily allow for such a risk factor by not sending officers who have undergone a trauma (e.g., confrontation with a fatal accident) promptly on to a subsequent incident (e.g., a corpse discovery) but by allowing them some time for rest instead. This also means the department could contact the officer, say, 3 weeks after the trauma to inquire how things are going.

Our results on neuroticism are inconsistent with those of, for instance, Breslau et al. (1991), who found that this factor increased vulnerability to PTSD in those who were exposed. However, we did find evidence for the presence of some other risk factors expressing personal predispositions, such as difficulty expressing personal feelings. This factor, by the way, correlated significantly with introversion, an insight that could be important for the preemployment psychological screening of police officers. Difficulty expressing feelings could be related, too, to the recently postulated type-D personality: the tendency to suppress emotional distress. A study by Denollet et al. (1996) has recently implicated this personality trait as an independent predictor of long-term mortality in patients with heart disease. Also, Evans et al. (1993) found that common coping strategies used by the police include keeping one's feelings to oneself, and they suggested that police officers may not be dealing effectively with their emotional reactions to occupational stress. This might in fact result from a process of depersonalization, which can involve the development of negative and cynical attitudes (Cambell et al., 1992). Difficulty expressing feelings could also reflect the role of a police culture that militates against the expression of emotions (Joyce, 1989; Kroes, 1985).

Some caveats should be mentioned with regard to this study. Our study on risk factors has focused on levels of posttraumatic stress symptomatology rather than on incidence of PTSD or other trauma-related disorders. It might also be argued that the police officers who responded to this study constituted a self-selective sample that may not be truly representative of police in general. For several reasons, however, we do not believe this to be the case. First, there was more than sufficient readiness within the police forces to take part in the study. We ended recruitment as soon as enough respondents had enlisted. Second, any possible bias due to “early birds” does not seem great, as there was no one deadline for recruitment: it was spread over about 2 years so that officers had sufficient opportunities to sign up. In the third place, the principal background variables of our respondents were consistent with those of the Dutch police force as a whole.

We generally endorse the conceptualization by Davidson and Foa (1993, p. 230), who have proposed a model under which the risk of developing PTSD is seen both as a function of the trauma (“external” factors) and as a function of the victim (“internal” factors). Certain extreme events (for instance, shooting incidents, disaster rescue work; Carlier and Gersons, 1992) that rise above a given severity threshold are likely to induce PTSD (at least initially) in most individuals regardless of predisposition (Kulka et al., 1990; Shore et al., 1986a, 1986b; Speed et al., 1989). At the opposite end of the scale, events that would be minimally stressful to most people (“lowmagnitude” events such as corpse discoveries; Carlier and Gersons, 1992) could prove traumatic in the presence of multiple predisposing factors (McFarlane, 1988a, 1988b, 1989). This formulation is consistent with the early theorizing about PTSD in DSM-I (Davidson, 1993, p. 152). The extent and the characteristics of such interaction between internal and external factors need to be investigated further (Davidson, 1993, p. 153).


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Accession Number: 00005053-199708000-00004