Although trauma exposure is common across the globe, there is marked variation among different countries in the incidence of specific events. At least four factors may influence cross-national differences. First, this divergence could reflect real differences in rates. For example, rape may be more common in high conflict zones and therefore result in higher prevalences (cf., higher rates among Liberian former combatants vs. noncombatants; Johnson et al. 2008). Second, there is cultural variation in the acceptability of reporting traumatic events, particularly sexual assault. Respondents’ embarrassment or fear of retaliation, which could be culturally mediated, likely influences reporting (e.g., Chan et al. 2013). Third, respondents might be less likely to report events that are considered normative. In this vein, regions in which one might expect more trauma exposure do not necessarily show a higher prevalence of traumatic events (e.g., marked variation in the prevalence of PTEs in postconflict settings; de Jong et al. 2001). Fourth, measurement issues, including inadequately worded questions, might also influence the accuracy of reports.

An additional consideration in making cross-study comparisons concerns variation in which traumatic events were assessed. Trauma inventories differ in both the number and types of events listed and each only provides information about the events that were included. More extensive inventories have been found to yield a higher prevalence of trauma exposure solely due to inclusion of additional events (Mills et al. 2011). Variation in which events are included is due in part to changing definitions of trauma in the Diagnostic and Statistic Manual of Mental Disorders (DSM). In the DSM-III and DSM-III-R, traumatic events were described as those that “occur outside the range of usual human experience.” In contrast, the DSM-IV and DSM-IV-R classified traumatic events as involving “actual or threatened death or serious injury, or threat to the physical integrity of self or others” (criterion A1), as well as an emotional response of “fear, helplessness, or horror” (criterion A2). This change increased prevalence of trauma exposure, although did not substantially alter the prevalence of posttraumatic stress disorder (PTSD) (Breslau and Kessler 2001). The recently released DSM-5 does not require an emotional response for an event to be considered traumatic, which is likely to further increase the prevalence of traumatic events.