In an initial report (Breslau et al., 1991), the evaluation of risk of exposure and risk of PTSD in exposed individuals demonstrated important sex differences. Females did have higher prevalence of PTSD than males. Females were somewhat less likely to be exposed to adverse traumatic events but were more likely to develop PTSD if exposed. Thus, an overall increased prevalence of PTSD in females must be accounted for by a significantly greater vulnerability to develop PTSD after exposure. Why is this?
Before we attempt to answer this question, it is important to examine the overall pattern of a lower burden of trauma in females than in males. The fact that women are exposed to fewer traumatic events obscures an important variation across "types of traumatic events." In the DAST (Breslau et al., in press), adverse events are classified into various categories: assaultive violence, other injury or shocking event, learning of traumas of others, and sudden unexpected death of relative or friend. The category with the highest rates of PTSD is assaultive violence.
Do females experience proportionately more assaultive events than males? The answer is no. Actually, males experience assaultive violence more frequently then females. Assaultive violence as a category is composed of rape, sexual assault other than rape, military combat, being held captive, being tortured or kidnapped, being shot or stabbed, being mugged, held-up, or threatened with weapons, and being badly beaten up. While females experience fewer assaultive events than males, they do experience significantly higher rates of one type of assaultive violence, namely rape and sexual assault.
Does a differential rate of rape and sexual assault between males and females account for the rates of PTSD? No. Females actually have higher rates of PTSD across all types of events in the assaultive violence category, both for events to which they are more exposed (rape) and for events to which they have less exposure (mugged, held-up, threatened with a weapon).
To provide a more quantitative picture from one study (Breslau et al., in press), the conditional risk of PTSD associated with exposure to any trauma was 13% in females and 6.2% in males. The sex difference in conditional risk of PTSD was due primarily to females' greater risk of PTSD following exposure to assaultive violence (36% versus 6%). Sex differences in three other categories of traumatic events (injury or shocking experience, sudden unexpected death, learning about traumas of a close friend or relative) were not significant.
Within the assaultive violence category, women had a higher risk of PTSD for virtually every type of event such as rape (49% versus 0%); sexual assault other than rape (24% versus 16%); mugging (17% versus 2%); held captive, tortured or kidnapped (78% versus <1%); or being badly beaten up (56% versus 6%).
To highlight these differences in PTSD risk, we can examine nonassaultive categories of events in both sexes. The single most frequent cause of PTSD in both sexes is sudden unexpected death of a loved one, but the sex difference was not large (this stressor accounted for 27% of female cases and 38% of male cases of PTSD in the survey). On the other hand, 54% of female cases and only 15% of male cases were attributable to assaultive violence.
Are there other differences between males and females with respect to PTSD? There are differences in the expression of the disorder. Women experienced certain symptoms more frequently then males. For example, females with PTSD more frequently experienced 1) more intense psychological reactivity to stimuli that symbolize the trauma; 2) restricted affect; and 3) exaggerated startle response. This is also reflected by the fact that females experienced a larger mean number of PTSD symptoms. This higher burden of symptoms was almost entirely due to the sex difference in PTSD following assaultive violence. That is, women with PTSD from assaultive violence had a larger burden of symptoms than did men with PTSD resulting from assaultive violence.