These changes in definition over time and between the classification systems have to be kept in mind when comparing prevalence rates of PTSD. The exposure to potentially traumatizing events and situations in the general population has been shown to exceed the number of persons who then develop a PTSD by far (Breslau 2009; Brewin et al. 2000; Keane et al. 2006). Kessler et al. (1995) examined 5,877 persons aged 15–54 years in the United States for the National Comorbidity Survey, a survey in the US general population which aimed to depict the overall prevalence of mental disorders in the community (Kessler et al. 1995). The lifetime prevalence rate for PTSD was 7.8 % for both genders, with 10.4 % higher in women than in men, where the rate was 5.0 %. In the follow-up survey, the National Comorbidity Survey Replication, Kessler et al. (2005) found a lifetime prevalence for PTSD of 6.8 % (Kessler et al. 2005). The highest lifetime prevalence Kessler et al. (2005) reported in the age-group 45–59 years with 9.2 % and the age-group 30–44 years with 8.2 %. In the Detroit area survey, a representative survey of 2,181 persons in the metropolitan area of Detroit, the risk of PTSD was highest when related to assaultive violence, with a rate of 35.7 % in women and 6.0 % in men, while the rate associated with any trauma was 13.0 % in women and 6.2 % in men (Breslau 2009). Criminal victimization, such as assault or rape, in women has been found to be associated with higher lifetime prevalence of PTSD with 26 % versus 12 % among those who did not experience these kinds of traumatic events (Keane et al. 2006).

The experiences prior and during migration may put refugees and asylum seekers under particular risk for the deterioration of mental health. So have studies suggested that refugees show elevated rates of anxiety and depressive disorders (Lindert et al. 2009). Fazel et al. (2005) performed a comprehensive review of psychiatric surveys which examined psychiatric disorders prevalence in refugee populations between 1966 and 2002 (Fazel et al. 2005). The authors included a total of 20 surveys with 6,743 persons from seven countries, including refugees from Southeast Asia, former Yugoslavia, the Middle East and Central America. The overall PTSD prevalence was 9 % (99 % Confidence Interval: 8–10 %). Fazel et al. found a great heterogeneity in the reported PTSD prevalences which could partly be explained by ethnicity, age, host country, duration of displacement, sample size, method of diagnosis and sampling and interview language. The authors further identified five studies on PTSD in children and adolescents, including data from 260 children from Bosnia, Central America, Iran, Rwanda and Kurdistan resettled in Canada, the United States and Sweden. The pooled prevalence rate of PTSD for refugee children in these studies was 11.0 % (99 % CI 7.0–17.0 %). Another systematic review focused on mental health in refugees, conducted by Steel et al. (2009), identified 145 surveys reporting estimates of PTSD prevalence in refugees and further examined the influence of torture on the these rates (Steel et al. 2009). The review included surveys published between 1980 and May 2009 of studies including populations aged 18 years and older, which had a minimum sample size of n = 50. Thus, a total of n = 64,332 persons were included in the meta-analysis on PTSD conducted by Steel et al. The PTSD prevalence rates ranged from 0 % to 99 %; the overall weighted PTSD prevalence across all surveys was 30.6 % (95 % CI 26.3–35.2 %). The prevalence of torture, which was reported by a subset of 84 surveys, was estimated to be 21.0 % (95 % CI 17.0–26.0 %). A meta-regression of factors associated with PTSD prevalence showed that experiences of torture explained the greatest intersurvey variance with 23.6 %. Surveys with a high rate of reported history of torture were associated with an odds ratio of 4.03 (95 % CI 2.31–7.04) for PTSD compared to surveys with a low rate (>40.0 % vs. <20.0 %). Surveys conducted within an ongoing conflict found a higher PTSD prevalence than those conducted in subsequent years (39.9 % vs. 2.3 years, 22.1 %; 3–5 years, 27.0 %; >5 years, 22.3 %). The countries/regions of origin with the highest PTSD prevalence were Africa (including 16 African nations; 33.5 %, 95%CI 14.2–60.7 %), Kosovo (31.6 %, 95 % CI 11.9–61.3 %) and Cambodia (30.3 %, 95 % CI 10.6–61.3 %). The lowest prevalence was found in one study of n = 2,422 persons in Vietnam with 10.0 %. High rates of PTSD have also been found in refugee populations exposed to political violence, such as, e.g. Armenian refugees from Azerbaijan who were exposed to the pogrom in Sumgait, Azerbaijan, in 1988 (Goenjian et al. 1994).