Posttraumatic stress disorder (PTSD) is characterized by symptoms of re-experiencing, avoidance and increased arousal following exposure to a traumatic event (American Psychiatric Association, 1994). Epidemiological studies indicate that PTSD has a 12-month prevalence of 1.33–3.5% (Creamer et al., 2001; Kessler et al., 2005) and a lifetime prevalence of 6.6–7.8% (Breslau et al., 1991, 1998; Kessler et al., 1995; Pietrzak et al., 2011; Resnick et al., 1993). It is often comorbid with other psychiatric disorders (Creamer et al., 2001; Pietrzak et al., 2011), and associated with substantial personal, economic and other societal costs (Kessler, 2000; Kessler et al., 2005).
