320 CHAPTER 7
People can be vulnerable to developing PTSD for a variety of reasons. For example,
people with severe mental disorders such as bipolar disorder (see Chapter 6) and schizo-
phrenia (Chapter 12) are also more likely to have PTSD, perhaps as a result of childhood
abuse or assaults that occurred during episodes of mental illness. However, PTSD may
go undiagnosed in this population (Mueser et al., 1998; Shevlin, Dorahy, & Adamson,
2007). PTSD is also more likely to develop in those who have some other type of anxi-
ety disorder (Copeland et al., 2007), perhaps because most anxiety disorders involve
hyperarousal and hypervigilance, which may lead people to respond to traumatic events
in ways that promote a stress disorder. In addition, people who experience a traumatic
event after having survived a prior traumatic event (for example, having been assaulted
and then, years later, living through a hurricane) may be at risk.
During the traumatic event, people who cope by dissociating (disrupting the
normal processes of perception, awareness, and memory) are more likely to develop
PTSD (Shalev et al., 1996).
After the traumatic event, classical conditioning and operant conditioning may
help to explain the avoidance symptoms of PTSD, in the same way that it can
explain such behavior in other anxiety disorders (Mowrer, 1939). In terms of clas-
sical conditioning, the traumatic stress is the unconditioned stimulus, and both in-
ternal sensations and external objects or situations can become conditioned stimuli,
which in turn can come to induce powerful and aversive conditioned emotional
responses (Keane, Zimering, & Caddell, 1985).
As with other anxiety disorders, the avoidant symptoms of PTSD are negatively
reinforced. In addition, drugs and alcohol can temporarily alleviate symptoms; such
substance use is also negatively reinforced, and explains why people with PTSD
have a higher incidence of substance abuse or dependence than do people who ex-
perienced a trauma but did not go on to develop PTSD (Chilcoat & Breslau, 1998;
Jacobsen, Southwick, & Kosten, 2001). In one study of National Guard members
who had been to Iraq, over half of those men and women who developed PTSD also
reported problem drinking (Alvarez, 2008).Targeting Social Factors
Social factors—both before the traumatic event and afterward—also help determine
whether PTSD develops. Such factors include the additional stress of lower socio-
economic status and the level of social support provided to the trauma victim.Socioeconomic Stress
As with other stressors in life, socioeconomic factors can infl uence an individual’s
ability to cope. People who need to worry about feeding, clothing, and housingCorbis/PunchstockAmong individuals who experienced a common
type of traumatic event—a car accident—those
who coped during the accident by dissociating
were more likely to go on to develop PTSD than
those who did not (Shalev et al., 1996). Other
factors that increase the likelihood of PTSD’s
developing after a car accident are ruminating
about the accident afterward, consciously trying
to suppress thoughts about it, and having intru-
sive, unwanted thoughts and memories about it
(Ehlers, Mayou, & Bryant, 1998).
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