502 TREATMENT OF SPECIFIC ANXIETY DISORDERS
lower rates have been reported in other countries such as Australia (Creamer et al.,
2001), Chile (Zlotnick et al., 2006), and Korea (Jeon et al., 2007). Based on the Ameri-
can studies, PTSD would be second only to specific and social phobia in terms of higher
prevalence in the general population.
Conditional Probability of PTSD
Since presence of trauma is a necessary criterion for PTSD, it is more meaningful to
determine rates of the disorder among individuals exposed to trauma. Numerous stud-
ies have been conducted on military samples in which risk of PTSD is directly related to
amount of combat exposure (e.g., Hoge et al., 2006; Ikin et al., 2007; Lee et al., 1995;
Tanielian & Jaycox, 2008). According to the National Vietnam Veterans Readjustment
Study (Kulka et al., 1990), 30.9% of men who served in Vietnam developed PTSD and
another 22.5% had partial PTSD, an extraordinarily high statistic that has come under
criticism (McNally, 2007b). A 50-year follow-up of Australian Korean veterans yielded
an estimated lifetime prevalence rate of 25.6% which was substantially higher than the
nonveteran comparison group (4.6%; Ikin et al., 2007). And a recent RAND study of
randomized telephone interviews with 1,965 veterans of Afghanistan and Iraq deploy-
ments concluded that 13.8% have a probable diagnosis of PTSD (Tanielian & Jaycox,
2008). Higher rates of PTSD have also been reported in firefighters (Corneil et al.,
1999) and international relief and development workers (Eriksson et al., 2001; see also
Whalley & Brewin, 2007). Clearly PTSD is an occupational hazard for those exposed
to higher rates of life- threatening experiences.
Numerous studies have also documented elevated rates of PTSD for individuals in
the general population exposed to trauma. In the NCS 20.4% of women exposed to
trauma had a lifetime probability of PTSD compared to 8.1% of trauma- exposed men
(Kessler et al., 1995). Approximately 20–25% of individuals exposed to serious injury,
motor vehicle accidents, or natural disasters like Hurricane Katrina (Galea et al., 2007)
or the 2004 tsunami in Sri Lanka (Hollifield et al., 2008) develop PTSD (e.g., Koren et
al., 1999; Mayou et al., 2001; Zatzick et al., 2007).
Trauma due to terrorism such as the 9/11 attacks on the World Trade Center or
the July 5, 2005, bombing in the London subway can cause an immediate increase in
distress and stress- related symptoms even in those not directly exposed to the trauma,
and these symptoms can persist for months, although at a significantly reduced level
(Rubin et al., 2007; Rubin, Brewin, Greenberg, Simpson, & Wessely, 2005; Silver et al.,
2002). However, individuals directly exposed to terrorists attacks will have especially
high rates of PTSD (30–40%) with 20% of exposed individuals continuing to experi-
ence symptoms 2 years later (Galea et al., 2002; North et al., 1999; see Whalley &
Brewin, 2007). Thus high rates of PTSD and its symptoms are evident immediately after
exposure to a life- threatening event, but 6 months later one-half to two- thirds of these
cases will remit, often without treatment (e.g., Foa & Rothbaum, 1998; Mayou et al.,
2001; Milliken, Auchterlonie, & Hoge, 2007; see Whalley & Brewin, 2007). And yet a
substantial number of individuals (i.e., one-third) who exhibited PTSD symptoms dur-
ing the acute phase of trauma exposure continue to experience a persistent and chronic
form of the disorder that is evident several months or years after exposure to trauma
(Kessler et al., 1995; see also Norris & Slone, 2007, for review).