Why does exposure to potentially traumatic events affect people differently?

It has long been recognized that people exposed to the same potentially traumatic events (PTEs) are affected differently. The majority of persons who experience a single PTE do not develop Posttraumatic Stress Disorder (PTSD). They may go on to experience other disorders, such as depression; however, some persons do not seem to be adversely affected by such exposure.

Several studies have been conducted to identify those factors that increase the risk that a person will meet criteria for PTSD following exposure to a PTE (e.g., Brewin, Andrews & Valentine, 2000; Bryant, Harvey, Guthrie & Moulds, 2003; Ozer, Best, Lipsey & Weiss, 2003). Risk factors that have been identified include, but are not limited to demographics, pre-trauma functioning, characteristics of the traumatic event, and posttraumatic factors such as social support.

Do Specific Risk Factors Lead to Different PTSD Trajectories?

Although factors that increase the chances that a given person will get PTSD following a PTE have been identified, it is not known whether specific risk factors will affect the way in which PTSD is experienced. For example, are there specific risk factors that lead to more severe symptoms of PTSD?

Recently, a study was conducted with 635 US peacekeepers (Dickstein, Suvak, Litz & Adler, 2010), where the researchers had two main goals. The first was to identify specific factors, such as pre-existing mental disorder, which could increase the risk of PTSD with these peacekeepers. The second goal was to identify whether there were specific risk factors that would be associated with different PTSD trajectories.

4 Proposed Trajectories

The researchers used a theoretical model proposed by Bonanno (2004), where he hypothesized four distinct ways in which PTSD could show up in affected individuals:

Bonanno proposed that persons who display the chronic trajectory tend to have the most severe symptoms following exposure to a potentially traumatic event (PTE). The symptoms tend to persist across time.

These individuals are proposed by Bonanno to have symptoms that are not very prominent or severe during the first 6 months following exposure to a PTE. With time, however, these individuals are thought to have an abrupt increase in the number and/or severity of symptoms.

These individuals are proposed to have an abrupt onset of symptoms following exposure to a PTE with the symptoms showing gradual improvement with time.

This group is proposed to consist of individuals who never have problems with their functioning following exposure to PTEs.

Risk Factors and Questionnaires

In the Dickstein, et al. study (2010), the group of 635 peacekeepers  had been deployed for 6 months to Kosovo in 2002. Prior to deployment (Time 1 or T1), they completed a variety of self-report questionnaires. They completed these same measures again during their last month in Kosovo  (T2), then again 3-4 months after they left Kosovo (T3), and again 8-9 months after leaving Kosovo (T4).  The peacekeepers reported that they experienced 1.65 PTEs on average while in Kosovo.

Risk factors that were examined in the study include  demographic variables (race, age, military rank, education), trauma exposure variables (previous exposure to PTEs, peacekeeping daily hassles, prior combat), psychiatric co morbidity variables (depression, aggressive behavior, alcohol use), personality variables (social closeness and stress reactivity),  coping strategy (behavioural, cognitive, avoidant, appraisal, religious, support seeking), and resting heart rate. The researchers measured symptoms of PTSD using the PTSD Checklist (PCL). Other measures included questionnaires to assess these risk factors.


The results supported 3 of the proposed trajectories by Bonanno (resilience, recovery, delayed). The chronic trajectory was not found; however, a fourth trajectory called unrealized anxiety was found with this group of peacekeepers.

Resilient Pathway
Eighty-four percent of the sample demonstrated a resilience pathway. These individuals showed consistently low levels of PTSD symptoms and there was no significant change over time in these symptoms. Resilience was associated with low levels of depression atT1 (pre-deployment), low peacekeeping daily hassles and low levels of previous trauma. The resilient pathway was also associated with less stress reactivity, less alcohol use and less aggressive behavior at T1.

Delayed Pathway
Three percent of the group demonstrated a delayed posttraumatic stress pathway. These individuals reported moderate PTSD symptom levels at Times 1 (pre-deployment) and 2 (final month in Kosovo), with a steady increase in symptoms at T3 and T4 (post-deployment). High levels of daily hassles during deployment and high levels of depression and alcohol use at pre-deployment were reported by this group.

Unrealized Anxiety Pathway
Nine percent of the sample of peacekeepers demonstrated a pathway named unrealized anxiety by the researchers.  This trajectory is characterized by relatively higher levels of PTSD symptoms at pre-deployment, with a marked decrease in symptoms during the last month of deployment and low symptom severity at post-deployment (T3 and T4). The researchers hypothesized that this group had a great deal of anticipatory anxiety at pre-deployment, which resulted in higher scores on the posttraumatic stress measure. These persons reported low levels of daily hassles and reported the highest overall levels of stress reactivity. In addition, they reported higher levels of previous trauma when compared to the resilient group, but no differences in previous trauma exposure than the other two groups. That is, the unrealized anxiety, delayed and recovery groups were not different from each other in previous trauma exposure; however, they had significantly more previous trauma exposure than the resilient group.

Four percent of the peacekeeping sample demonstrated a recovery pathway, characterized by low symptom severity at pre-deployment, high symptom severity during the last month in Kosovo and high symptom severity 3-4 months post-deployment. They had a return to baseline at 8-9 months post-deployment.  The recovery trajectory was associated with high levels of daily hassles.

What does this mean?

The results of this one study provide some interesting information on how various risk factors may affect the course of PTSD with a sample of military peacekeepers. There were several limitations to this study that may have affected the results. The researchers tracked PTSD for only 10 months; however, the course of PTSD over longer periods of time is also of interest and results could change if longer follow-up periods are studied.

This study needs to be conducted with different samples to determine whether the results would be the same. For example, the risk factors and/or PTSD trajectories could differ depending on the sample being examined. Individuals who are exposed to combat may have different results, as could other types of trauma-exposed samples, such as interpersonal violence, motor vehicle accidents, natural disasters, emergency service personnel, medical trauma, and others.  Moreover, the majority of the peacekeepers in this sample were male, and thus it is not know whether gender posed a risk factor in this study or how gender may relate to various trajectories.

So we cannot conclude that these particular risk factors and symptom trajectories would be the same for other peacekeeping samples or for other types of trauma exposure. More study is necessary to draw firmer conclusions.  If similar results are found for peacekeepers and/or other samples, there are treatment implications. For example, individuals who are high in anticipatory anxiety may benefit from treatments that reduce baseline anxiety levels, and this in term may serve a protective factor against the development of PTSD if the person is exposed to a PTE.


Bonanno, G.A. (2004). Loss, trauma, and human resilience. Have we underestimated the human capacity to thrive after aversive events? American Psychologist, 59, 20-28.

Brewin, C.R., Andrews, B., & Valentine, JD (2000).  Meta-analysis of risk factors for posttraumatic stress disorder in trauma-exposed adults. Journal of Consulting and Clinical Psychology, 68, 748-766.

Bryant, R.A., Harvey, A.G., Guthrie,  R.M., Moulds, M.L. (2003).  Acute psychophysiological arousal and posttraumatic stress disorder: A two-year prospective study. Journal of Traumatic Stress, 16, 439-443.

Dickstein, B.D, Suvak, M., Litz, B.T., Adler, A.B. (2010). Heterogeneity in the Course of Posttraumatic Stress disorder: Trajectories of Symptomatology. Journal of Traumatic Stress, 23, 331-339.

Ozer, E.J.,  Best, S.R., Lipsey, T.L., & Weiss, D.S. (2003).  Predictors of posttraumatic stress disorder and symptoms in adults: A meta-analysis. Psychological Bulletin, 129, 52-73.

About the Author

Anne Dietrich, PhD, R.Psych. Dr. Dietrich (www.annedietrich.ca) has a private practice in Richmond and Vancouver. She is Past Chair of the Traumatic Stress Section of the Canadian Psychological Association and is a reviewer for the Journal of Traumatic Stress.

Why does exposure to potentially traumatic events affect people differently?

Anne Dietrich, PhD, R.Psych. Dr. Dietrich (www.annedietrich.ca) has a private practice in Richmond and Vancouver. She is Past Chair of the Traumatic Stress Section of the Canadian Psychological Association and is a reviewer for the Journal of Traumatic Stress.





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