Why Do Some Develop PTSD and Some Do

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Figuring out why some people develop PTSD and some do not after exposure to a traumatic stressor requires an understanding of the risk factors. Is it personality? Could it be genetic? Why do some people seem to be traumatized over and over again? Some seemingly trivial events have led to PTSD. When this is the case, personal vulnerability and risk factors become tantamount. A stressor alone is rarely enough to produce psychopathology.

There are three large categories of risk factors, pretrauma, peritraumatic, and posttraumatic. It is also important to keep in mind that the risk factor issue is not as clear-cut as it might at first seem. Certainly, if someone possesses risk factors, he or she would be considered more likely to develop PTSD. But what if someone has 2, 3, or 10 risk factors? Is he or she 2 times or 10 times more likely to develop PTSD? The answer is we don't know. The risk factor issue is not a simple additive model, with the more risk factors you have adding up to PTSD. This may be the case, and it does make sense logically and even clinically. A clinician or professional working in prevention might want to operate on this assumption. But for now, most research looks at the various risk factors in isolation, and each should be considered an individual risk factor in and of itself.

Exposure Risk

Some people are exposed to traumatic stressors more than others. Certainly, a soldier serving combat is at a higher risk than a gardener. Being at a higher risk for exposure to a traumatic stressor is an obvious but sometimes overlooked risk factor. The lifetime prevalence of exposure to a traumatic stressor or event in a general population sample has been estimated to be 39.1 percent (Breslau, Davis, Andreski, Federman, & Anthony, 1998). Almost 40 percent of us have been exposed.

Exposure risk can be broken down into more specific categories. Exposure rates for men are higher than for women in general, but exposure rates to sexual violence are higher for women, and the lifetime prevalence of PTSD is higher in women. Persons with lower education levels, especially those who have not finished high school, have higher exposure rates than college graduates.

The most dangerous jobs, according to a CNN poll, include the following: timber cutters, fishers, pilots and navigators, structural metal workers, driver-sales workers, roofers, electric power installers, farm workers, construction laborers, and truck drivers. The literature, however, shows no research has been done on PTSD in many of these occupations, with the exception of motor vehicle accident-related PTSD. One study done with construction workers exposed to a fatal work accident showed that 26.8 percent of 41 subjects met criteria for PTSD postaccident (Hu, Liang, Hu, Long, & Ge, 1999).

According to Haslam and Mallon (2003), emergency workers are at high risk for developing PTSD. Emergency workers are exposed to traumatic stressors on a daily or weekly basis. Consider Table 4.1, adapted from Figley (1995).

Clohessy and Ehlers (1999) found that 21 percent of ambulance drivers in their study of 56 persons met criteria for PTSD. Robinson, Sigman, and Wilson (1997) found that 13 percent of a sample of 100 suburban police officers met criteria for PTSD. A study done with resident physicians found that 13 percent met criteria for PTSD. Eriksson, van de Kemp, Gorsuch, Hoke, and Foy (2001) found that approximately 30 percent of international relief and development workers showed significant symptoms of PTSD. Ultimately, one can conclude from these studies that certain occupations put participants at increased risk for PTSD, above the expected prevalence rates ranging from 1 to 14 percent in the DSM-IV.


Secondary Traumatic Stress Exposure


Personal direct exposure to life-threatening trauma

Body handling

Direct or indirect secondary exposure









Law enforcement officers




Rescue workers




Are some people more exposed to violence than others? A history of criminal victimization is a significant risk factor for subsequent victimization (Koss & Dinero, 1989; Norris & Kaniasty, 1992; Sorenson, Siegel, Golding, & Stein, 1991; Steketee & Foa, 1987; Wyatt, Guthrie, & Notgrass, 1992).

The personality trait of sensation seeking has been implicated in increased exposure risk. Zuckerman et al. (1979) define sensation seeking as the need for varied, novel, and complex sensations and experiences and the willingness to take physical and social risk for such experiences. This has been associated with Substance Abuse, which itself is an exposure risk factor. The personality traits of Extroversion and Neuroticism are exposure risk factors (Breslau, Davis, & Andreski, 1995). McNally (2003) states, "outgoing, stress prone people were exposed to trauma more often than retiring, calm people."

An interesting question has been researched asking whether having a preexisting mental disorder increases one's risk for exposure to traumatic stressors or events. Research has shown that someone with a prior history of major depression and illicit drug use is at a higher risk for exposure to traumatic stressors.

Finally, Dohrenwend (1998) and McNally (2003) report that being African American, having a family history of psychiatric illness, having a childhood history of conduct problems, having a history of prior traumatic event exposure, having a history of Major Depression, and having a history of drug or Alcohol Abuse puts someone at greater risk for exposure. This issue of race has been found to be significant with respect to combat exposure. Minority status has been shown to be a risk for combat and war exposure and thus higher risk for PTSD (Green, Grace, Lindy & Leonard, 1990; MacDonald, Chamberlain, & Long, 1997).

Individual Risk Factors for PTSD

Ozer, Best, Lipsey, and Weiss (2003) reviewed 23 studies that showed a small but significant relationship between history of prior trauma and PTSD symptoms or diagnosis. This relationship differed significantly depending on the type of stressor: When the trauma was noncombat, interpersonal violence such as assault, rape, or domestic violence was more strongly related to future PTSD than combat exposure was.

People with a lifetime history of PTSD typically have at least one other mental disorder (Breslau, Davis, et al., 1998). Specifically, preexisting Major Depression and any Anxiety Disorder increase the risk for PTSD following exposure to a traumatic event.

Prior adjustment problems including previous mental health treatment, pre-trauma emotional problems, pretrauma Anxiety Disorder or affective disorders, and Antisocial Personality Disorder prior to military service are risk factors (Ozer et al. 2003). Further, having prior adjustment problems was more related to PTSD when the trauma was noncombat interpersonal violence or accident than combat exposure and when the adjustment problems were closer in time to the trauma. In the same review, psychopathology in family of origin in 9 studies showed a relationship to future PTSD, especially with noncombat interpersonal violence.

Are people who suffer from serious physical health problems, injuries, or terminal illness at risk for PTSD? Some research suggests that the rates of PTSD in persons with specific illnesses are higher than general rates. Kelly et al. (1998) report that 30 percent of 61 men informed that they were human immunodeficiency virus (HIV) positive met criteria for PTSD in response to their diagnosis. That is more than twice the rate prevalence rate in the DSM-IV. In 100 post-myocardial infarction patients, 16 percent were suffering from PTSD (Kutz, Shabtai, Solomon, & Neumann, 1994). In women with breast cancer studied by Leiderman-Cerniglia (2002), 9 to 14 percent of women with cancer met criteria for PTSD. In 109 survivors of serious physical injury requiring hospitalization, 32 percent met criteria for high levels of PTSD (Richmond & Kauder, 2000).

Pretrauma personality features such as certain types of personal schemas about the self, others, or the world have been implicated in the course of PTSD. Elliot and Lassen (1997) identified inflexible schemas, and Riggs and Foa (1993) identified overvalued schematic representations, which are rigid beliefs in one's absolute safety of the world and the invulnerability of the self. There are negative pretrauma schemas (Beck, Rush, Shaw, & Emery, 1979). Mardi Horowitz (2004) implicates pretrauma personality types with the basic idea that people with balanced pretrauma schemas of world, self, and others that are not too overvalued and not too negative will go through a healthier readjustment process. After an initial period of disruption and posttraumatic symptomology, there is a normative and gradual assimilation of trauma-related information and ultimate resolution without development of PTSD. Overvalued schemas lead to vulnerability and more posttraumatic distress.

The personality factors of Extroversion and Neuroticism as measured by the Eysenck Personality Inventory have been found to be relevant premorbid factors in which PTSD groups are higher in Neuroticism and lower in Extroversion than non-PTSD individuals (McFarlane, 1988).

Studies done with the Minnesota Multiphasic Personality Inventory have found that characteristics of psychopathic deviancy, and hypochondriasis, were relevant premorbid factors measured many years before the occurrence of a traumatic stressor^) (Schnurr, Friedman, & Rosenberg, 1993).

In research looking at the genetic risk, PTSD is more prevalent in monozygotic twins versus dizygotic twins (Skre et al., 1993). True and Lyons (1999) report that 13 to 30 percent of the variance in reexperiencing symptoms, 30 to 34 percent in avoidance symptoms, and 28 to 32 percent in arousal symptoms can be accounted for by genetics.

Perhaps some people have a psychobiological vulnerability to PTSD. Carlson and Dalenberg (2000) propose the existence of a nongenetic biological predisposition that determines varied responses to the same stressor. Biological changes in response to prior trauma can shape responses to future traumas. Vaiva et al. (2004) found that individuals with low plasma-gamma-aminobutyric acid levels involved in the regulation of the intensity and the duration of the central hyperadrenergic response in times of high stress were more prone to PTSD following exposure to a traumatic stressor.

Carlson and Dalenberg (2000) report that children at earlier stages of development will have more extreme responses because of their lack of coping resources. The emotional developmental stage can be important; has the child has formed a secure attachment. Insecure attachment is a risk factor, especially if the trauma involves an attachment figure. Better cognitive, behavioral, and social skills can enable better coping, social support acquisition, and control and help prevent future trauma through better planning and avoidance. Traumatic experiences earlier on have a more pervasive impact, and symptoms can interfere with healthy development, thus having a twofold effect on future trauma reactions.

Group Risk Factors

Are there certain groups or sociological categories that being a member of puts one at an increased risk for PTSD? Norris et al. (2003) hypothesized that in poor countries, factors such as physically demanding and dangerous work; inferior and overcrowded housing; extreme subsistence hardship; and high power differentials between rich and poor, women and men, and adults and children put people in these countries at a higher risk for exposure to traumatic bereavement, life-threatening accidents, interpersonal violence, and, thus, higher rates of PTSD. In their study of four cities in Mexico, lifetime prevalence of exposure was 76 percent, and prevalence of PTSD was 11.2 percent. Risk for PTSD was highest in the poorest city, persons of lower socioeconomic status (SES), and women. Although still within the range of 1 to 14 percent from the DSM-IV, subjects in this study were at the higher end of this range. Davidson, Hughes, Blazer, and George (1991) sampled approximately 3,000 subjects in one community and found that of those sampled who had PTSD-related symptoms, they had higher rates of job instability and parental poverty.

Although men are exposed to traumatic stressors overall more often, women are more likely than men to develop PTSD (Kessler et al., 1995). Women are more likely to develop chronic forms of the disorder as well (Breslau, Kessler, et al., 1998). Different hypotheses as to why this is the case have been put forward with inconclusive empirical results: greater physiological reactivity in women; different levels of interpersonal violence in women; higher levels of poverty, discrimination, and oppression in women (Breslau, Kessler, et al., 1998; Shalev, Orr, & Pitman, 1993; Wolfe & Kimerling, 1997).

Being a victim of violence and crime increases one's chance of PTSD (Norris, 1992; Kilpatrick et al., 1989; Resnick et al., 1993). A history of rape is one of the highest risk factors of PTSD (Breslau, Davis, Andreski, & Peterson, 1991; Resnick et al., 1993). Elevated risk for PTSD can vary with the type of crime to which one is exposed. In essence, however, a victim's perception that his or her life is threatened or that he or she is actually injured is associated with increased risk (Kilpatrick et al., 1989).

Finally, Brewin, Andrews, and Valentine (2000) conducted a meta-analysis of risk factors and found that female gender, greater social disadvantage, greater educational disadvantage, greater intellectual disadvantage, psychiatric history, and various types of personal adversity are all significant risk factors. These investigators note, however, that the effect size for each of these is relatively low when compared to factors happening during or immediately after the trauma, such as trauma severity, lack of social support, and additional life stress posttrauma.

Peritraumatic Risk Factors

How one acts, thinks, and feels during an actual traumatic event have been found critical in predicting the future development of PTSD. When dissociative symptoms emerge or a person has a dissociative experience during the actual event, known as peritraumatic dissociation, the risk of future PTSD development is higher (Candel & Merckelbach, 2004). Ozer et al. (2003) state that peritraumatic dissociation is the strongest predictor of future PTSD symptoms.

Research has also found that the degree to which someone perceives his or her life to be at risk during the actual stressor is a peritraumatic risk factor. Ozer et al. (2003) reviewed 12 studies showing a significant and strong relationship between perceived life threat and future PTSD diagnosis or symptoms.

In a review of studies looking at peritraumatic emotional responses, Ozer et al. (2003) found that persons who report having very intense negative emotional responses during or immediately after a traumatic event had higher levels of PTSD symptoms. The emotions reported in the studies were fear, helplessness, horror, guilt, and shame.

Posttrauma Risk Factors

O'Brien and Hughes (1991) propose that there is a general agreement that events following exposure to a traumatic stressor play a significant role in determining whether someone develops PTSD or PTSD-related symptoms.

Many Vietnam veterans report that when they came home from the war they encountered a hostile and unwelcoming environment. This report and similar observations by people have in part spurred mobilizations to be more supportive of United States military personnel in subsequent conflicts. Research has shown that negative homecoming experiences were found to be more associated with PTSD than positive homecoming experiences (Butler et al., 1988). The same finding was made with British soldiers returning home from the Falkland Islands (O'Brien & Hughes, 1991).

Posttraumatic Stress Disorder has been repeatedly associated with lower levels of perceived social support in both civilian and veteran populations (Barrett & Mizes, 1988; Bowler, Mergler, Huel, & Cone, 1994; Solomon, Mikulincer, & Avitzur, 1988). Ozer et al. (2003) state that perceived social support is one of the strongest predictors.

According to McFarlane and Yehuda (1996), how one adapts to disruption of the acute and chronic symptoms of PTSD is a risk factor: "The ability to tolerate suffering is therefore a critical determinant of long-term adaptation" (p. 157). The ability to tolerate fear and loss and to effectively cope with the demoralization of hyperarousal and the progressive disruption of the individual's neurobi-ological functioning play an increasing role in understanding the nature and course of PTSD above and beyond the original traumatizing event or events.

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