**3. Possible explanations for sex differences in the prevalence of PTSD**

### **3.1 Sex differences in exposure to potentially traumatic events**

The finding that more females than males develop PTSD has been reported independently of study type, population studied, culture, type of assessment, and other methodological variables (Tolin & Foa, 2008). Thus, the increased prevalence of PTSD in females compared to males does not appear to be simply a product of measurement error or methodological bias. Chung and Breslau (2008) conducted a latent class analysis and found no evidence of differential symptom reporting in males compared to females. This led them to the conclusion that the increased symptomatology reported by females is likely to reflect a substantive difference, rather than a sex-related reporting bias. Instead, it has been suggested that as a result of the different gender roles, which males and females hold in

Males are exposed to more potentially traumatic events (PTE's) than females (Tolin & Foa, 2008), particularly in adolescence and young adulthood (Norris et al., 2007). In the National Comorbidity Survey, 60.7% of males and 51.2% of females reported at least one PTE, and significantly more males than females reported exposure to more than two trauma types (Kessler et al., 1995). Despite the finding that males are more likely to experience a PTE and experience more types of PTE's than females, the female-male ratio in the prevalence of PTSD is approximately 2:1 (Tolin & Foa, 2008) with females reporting higher levels of both re-experiencing, avoidance, and arousal (Ditlevsen & Elklit, 2010). The lifetime prevalence of PTSD is 10.4% for females and 5.0% for males and the conditional risk across trauma types is 20.4% for females and 8.2% for males (Kessler et al., 1995). Sex differences in the prevalence of PTSD become evident early in life, peak in early adulthood, and become weakened with increased age (Ditlevsen & Elklit, 2010; Norris et al., 2002). Across studies, the increased prevalence of PTSD in females compared to males appears to be particularly evident for lifetime PTSD (Tolin & Foa, 2008), indicating that PTSD tends to be of longer duration in females than in males, and in the Detroit Area Survey of Trauma the median time from onset of PTSD to remission was four years for females compared to one year for males

Despite findings that sex differences in PTSD have been found across cultures and thus appear to be culturally persistent, variations regarding how pronounced such sex differences are have been reported. Norris et al. (2001) compared sex differences in a Mexican, an African-American, and an Anglo-American sample and found that sex differences in the prevalence of PTSD were amplified in the Mexican sample and attenuated in the African-American sample, with the Anglo-American sample falling in between (Norris et al., 2001). It has been suggested that sex differences in PTSD are particularly evident in communities that emphasise traditional gender roles (Norris et al., 2007). This suggests that social gender and biological sex are both important in making up such differences. Interestingly, the cross-cultural variations on sex differences appear to be more pronounced for intrusion and avoidance than for arousal symptoms, which are thought to be rooted in biological processes. It is thus possible that sex differences in arousal are primarily related to biological sex, whereas sex differences in avoidance and intrusion are

**3. Possible explanations for sex differences in the prevalence of PTSD** 

The finding that more females than males develop PTSD has been reported independently of study type, population studied, culture, type of assessment, and other methodological variables (Tolin & Foa, 2008). Thus, the increased prevalence of PTSD in females compared to males does not appear to be simply a product of measurement error or methodological bias. Chung and Breslau (2008) conducted a latent class analysis and found no evidence of differential symptom reporting in males compared to females. This led them to the conclusion that the increased symptomatology reported by females is likely to reflect a substantive difference, rather than a sex-related reporting bias. Instead, it has been suggested that as a result of the different gender roles, which males and females hold in

**3.1 Sex differences in exposure to potentially traumatic events** 

**2. Sex differences in PTSD prevalence** 

(Breslau et al., 1998).

also affected by social gender.

society, men and women are exposed to different stressors on a day-to-day basis (Barnyard & Graham-Bermann, 1993; Ptacek et al., 1992). This structural theory is likely to influence not only the types of traumatic events males and females are exposed to, but also how they generally respond to such events. Thus, one possible explanation for the sex difference in the prevalence and severity of PTSD is that males and females differ in the types of trauma they experience. A well-conducted meta-analysis by Tolin and Foa (2008) found that across studies, more males than females are exposed to accidents, non-sexual assaults, combat or war, disasters, illness, unspecified injuries, and witnessing the death or injury of others. In contrast, more females experience sexual assault and childhood sexual abuse (CSA). However, it should be kept in mind that these findings are based simply on whether or not the subjects report having been exposed to the different types of PTE's. Males and females may not only be subject to different reporting bias, but may also differ in the number of times they have been exposed to each event, and such differences are unlikely to be identified in this type of meta-analysis. Thus, even though females are less likely overall to be subjected to non-sexual assaults, overall, it is possible that females who are exposed tend to be assaulted repeatedly, such as is often the case in domestic violence. It remains to be seen, whether such differences in multiple exposures to the same type of PTE add to the sex difference in PTSD prevalence. In addition to an increased risk of sexual assault, females also appear to be more exposed to betrayal trauma, in that more females than males report having been exposed to interpersonal trauma, especially assault by a perpetrator close to the victim (Goldberg & Freyd, 2006).

Certain types of trauma (e.g. rape, CSA, combat) have been found to be more toxic (i.e. more likely to lead to PTSD) than others (e.g. accidents, bereavement; Kessler et al., 1995). It is therefore possible that the increased risk of sexual trauma in childhood, adolescence, and adulthood in females may account for differences in PTSD prevalence. However, studies have found that sex differences in PTSD prevalence persist even after trauma type is controlled, indicating that the high prevalence of PTSD in females is not simply a result of increased exposure to sexual trauma (Kessler et al., 1995; Tolin & Foa, 2008). However, even though studies have shown that sex differences in PTSD prevalence exist across trauma types, sexual assault prior to the index trauma is rarely controlled for and may still contribute to the increased PTSD prevalence in females following new traumas. Furthermore, even within the same type of trauma, males and females may differ in the characteristics as well as their interpretation of the event (Tolin & Foa, 2008). For example, a woman who is robbed in an isolated spot may fear that the robber will also rape her and thus have a stronger physiological reaction than a man in the same situation, who may be less likely to interpret the event as anything more than a robbery, although males as well as females may interpret the event as highly threatening and even fear for their lives.

Interestingly, studies based on military and police samples have generally failed to find an increased risk of PTSD in females compared to males (Lilly et al., 2009). Although male and female military veterans generally differ in the types of events they have been exposed to, it is also possible that the lack of reported sex difference is related to one or more variables on which police and military females differ from female civilians. Furthermore, the metaanalysis by Tolin and Foa, (2008) found that a significant sex difference in PTSD rates has not been established following adult and childhood sexual assault and abuse. This failure to discover significant sex differences in PTSD following sexual assault and abuse may be accounted for by the relatively low number of both-sex studies focusing on these two

disorders, including depression and anxiety disorders (Hettema et al., 2004; Kendler et al., 2004). The influence of negative affectivity on all three disorders may explain, why both anxiety and depression have been found to be related to PTSD (Kessler et al., 1995). Females have been reported to score higher than males on measures of neuroticism (Hettema et al., 2004; Lynn and Martin, 1997) and negative affectivity (Joiner & Blalock, 1995), and both anxiety and depression are more commonly found in females than in males (Kessler et al., 1994). It could therefore be hypothesised that the higher prevalence of PTSD in females is a result of their higher negative affectivity/neuroticism as well as pre-existing anxiety and depression. One study has reported that the higher risk of PTSD in females in the general population was mainly due to their exposure to more toxic trauma types in combination with a higher prevalence of pre-existing psychiatric disorders (Hapke et al., 2006). However, Spindler et al. (2010) found that even though sex was no longer significantly associated with PTSD status after trait anxiety was controlled for, there was still a trend towards significance, and Fullerton et al. (2001) found that neither prior PTSD, major depression, nor other anxiety disorders could account for the increased PTSD prevalence in females. Finally, Breslau et al. (1997) found that although prior depression and anxiety disorder did reduce the sex difference in PTSD prevalence, they did not eliminate it. Thus, at the present time there is not convincing evidence that sex differences in PTSD can be fully accounted for by

In relation to the risk factors related directly to the traumatic event, sex differences have been widely reported in primary appraisal, and it has been suggested that the higher risk for stress-related disorders in females may be due to such differences. The A2 criterion of the DSM-IV PTSD diagnosis states that in order for an event to be considered traumatic, the person must have experienced intense fear, horror, or helplessness (American Psychiatric Association, 2000). Females have generally been found to be more likely than males to report such feelings in response to a PTE (Irish et al., 2011; Norris et al., 2002). Another common peritraumatic experience is dissociation, which is defined as a disruption in the usually integrated functions of consciousness, memory, identity, and perception (American Psychiatric Association, 2000). Dissociative reactions during or following a traumatic event have been found to be important risk factors for PTSD (Ehring et al., 2006; Ozer et al., 2003). Although there do not appear to be major sex differences in the prevalence of dissociative reactions in the general population (Spitzer et al., 2003), several studies have reported higher levels of trauma-related dissociation in females compared to males (Bryant & Harvey, 2003; Irish et al., 2011). It is thus possible that sex differences in such peritraumatic rections may

It has been suggested that the professional training of police officers, which is in accordance with a traditionally masculine minimisation of emotional reactivity, can account for the previously mentioned lack of reported sex differences in PTSD prevalence in police samples (Pratchett et al., 2010), which appears to be caused by a lower degree of traumatisation in female police officers compared to female civilians. Lilly et al. (2009) compared female police officers to female civilians and found that despite a higher degree of traumatic exposure, female police officers reported lower levels of PTSD. This could be accounted for by lower levels of peritraumatic emotional distress in the police officers. However, although female police officers also reported lower levels of peritraumatic dissociation, this did not

negative affectivity/neuroticism and pre-existing symptomatology.

**3.2.2 Peritraumatic risk factors** 

account for sex differences in PTSD prevalence.

trauma types. Furthermore, males are more often assaulted by numerous perpetrators and sustain more physical injuries, both of which could add to the prevalence of PTSD in males compared to females (Tolin & Foa, 2008). However, another possibility is that there may be a ceiling effect, whereby high levels of PTSD following particularly toxic traumas (e.g. sexual assault, combat) in males as well as females will overrule any specific female vulnerability to traumatic stress (Gavranidou & Rosner, 2003). Although it is too soon to rule out this possibility, one study published after Tolin and Foa's meta-analysis found that adult female victims of childhood abuse and neglect were significantly more likely to meet criteria for a PTSD diagnosis than males (Koenen & Widom, 2009), suggesting that sex differences may exist in these types of traumas. Even more importantly, this sex difference was reduced but not eliminated when later rape and exposure to multiple traumas were controlled for. Similarly, a Danish study found that sex remained a significant predictor of lifetime PTSD symptoms in students after rape was controlled for (O'Connor & Elklit, 2008), although the way in which rape was assessed might have underestimated the true degree of sexual victimisation in the sample.

To sum up, although the extent of sex differences in PTSD following highly toxic trauma types needs to be studied more thoroughly, the increased risk of PTSD in females has been established across a wide variety of trauma types. Although the increased exposure of females to sexual assault and CSA may add to the sex difference in the prevalence of PTSD, differences in exposure to traumatic events do not appear to fully account for these differences. It thus appears that the structural theory is not sufficient to account for the observed sex differences in PTSD. Instead, the mediation hypothesis suggests that females are more vulnerable to PTSD, because they exhibit higher levels of certain risk factors associated with PTSD. From a gender based perspective on coping with traumatic stress, the socialisation theory holds that the way men and women are brought up and continue to be socialised in a context of gender role expectations affect how they react in the face of trauma (Ptacek et al., 1992; Rosario et al., 1988). As a result, men and women differ in the kind of events they interpret as threatening, and consequently their preferred coping strategies as well as the physiological reactions are likely to differ (Simmons & Granvold, 2005). Thus, according to both the socialisation theory and the mediation hypothesis, sex differences in PTSD prevalence may be related to sex differences in associated risk factors in the time leading up to, during, and following the traumatic event. Next, we will focus on some risk factors, which are more pronounced in females than in males, and which according to the mediation hypothesis may help account for the increased PTSD prevalence in females. Risk factors, which are not hypothesised to add to the higher PTSD severity in females, compared to males (e.g. social support, prior trauma exposure) will not be discussed here.

#### **3.2 Sex differences in risk factors related to the development of PTSD 3.2.1 Pre-traumatic risk factors**

It has been suggested that the higher degree of negative affectivity in females may result in more reactive emotional and somatic responses in females compared to males (Zeidner, 2006). The overlapping constructs of negative affectivity and neuroticism have been defined as the propensity to experience a wide variety of somatic and emotional dysphoric states including depression, anxiety, anger, and somatic symptoms (Kirmayer et al., 1994). High levels of neuroticism have been shown to increase sensitivity to stressful life events (Kendler et al., 2004). Furthermore, neuroticism and negative affectivity have been shown to play a role in the development of PTSD (Ahern et al., 2004) as well as in other psychiatric

trauma types. Furthermore, males are more often assaulted by numerous perpetrators and sustain more physical injuries, both of which could add to the prevalence of PTSD in males compared to females (Tolin & Foa, 2008). However, another possibility is that there may be a ceiling effect, whereby high levels of PTSD following particularly toxic traumas (e.g. sexual assault, combat) in males as well as females will overrule any specific female vulnerability to traumatic stress (Gavranidou & Rosner, 2003). Although it is too soon to rule out this possibility, one study published after Tolin and Foa's meta-analysis found that adult female victims of childhood abuse and neglect were significantly more likely to meet criteria for a PTSD diagnosis than males (Koenen & Widom, 2009), suggesting that sex differences may exist in these types of traumas. Even more importantly, this sex difference was reduced but not eliminated when later rape and exposure to multiple traumas were controlled for. Similarly, a Danish study found that sex remained a significant predictor of lifetime PTSD symptoms in students after rape was controlled for (O'Connor & Elklit, 2008), although the way in which rape was assessed might have underestimated the true degree of sexual

To sum up, although the extent of sex differences in PTSD following highly toxic trauma types needs to be studied more thoroughly, the increased risk of PTSD in females has been established across a wide variety of trauma types. Although the increased exposure of females to sexual assault and CSA may add to the sex difference in the prevalence of PTSD, differences in exposure to traumatic events do not appear to fully account for these differences. It thus appears that the structural theory is not sufficient to account for the observed sex differences in PTSD. Instead, the mediation hypothesis suggests that females are more vulnerable to PTSD, because they exhibit higher levels of certain risk factors associated with PTSD. From a gender based perspective on coping with traumatic stress, the socialisation theory holds that the way men and women are brought up and continue to be socialised in a context of gender role expectations affect how they react in the face of trauma (Ptacek et al., 1992; Rosario et al., 1988). As a result, men and women differ in the kind of events they interpret as threatening, and consequently their preferred coping strategies as well as the physiological reactions are likely to differ (Simmons & Granvold, 2005). Thus, according to both the socialisation theory and the mediation hypothesis, sex differences in PTSD prevalence may be related to sex differences in associated risk factors in the time leading up to, during, and following the traumatic event. Next, we will focus on some risk factors, which are more pronounced in females than in males, and which according to the mediation hypothesis may help account for the increased PTSD prevalence in females. Risk factors, which are not hypothesised to add to the higher PTSD severity in females, compared

to males (e.g. social support, prior trauma exposure) will not be discussed here.

It has been suggested that the higher degree of negative affectivity in females may result in more reactive emotional and somatic responses in females compared to males (Zeidner, 2006). The overlapping constructs of negative affectivity and neuroticism have been defined as the propensity to experience a wide variety of somatic and emotional dysphoric states including depression, anxiety, anger, and somatic symptoms (Kirmayer et al., 1994). High levels of neuroticism have been shown to increase sensitivity to stressful life events (Kendler et al., 2004). Furthermore, neuroticism and negative affectivity have been shown to play a role in the development of PTSD (Ahern et al., 2004) as well as in other psychiatric

**3.2 Sex differences in risk factors related to the development of PTSD** 

victimisation in the sample.

**3.2.1 Pre-traumatic risk factors** 

disorders, including depression and anxiety disorders (Hettema et al., 2004; Kendler et al., 2004). The influence of negative affectivity on all three disorders may explain, why both anxiety and depression have been found to be related to PTSD (Kessler et al., 1995). Females have been reported to score higher than males on measures of neuroticism (Hettema et al., 2004; Lynn and Martin, 1997) and negative affectivity (Joiner & Blalock, 1995), and both anxiety and depression are more commonly found in females than in males (Kessler et al., 1994). It could therefore be hypothesised that the higher prevalence of PTSD in females is a result of their higher negative affectivity/neuroticism as well as pre-existing anxiety and depression. One study has reported that the higher risk of PTSD in females in the general population was mainly due to their exposure to more toxic trauma types in combination with a higher prevalence of pre-existing psychiatric disorders (Hapke et al., 2006). However, Spindler et al. (2010) found that even though sex was no longer significantly associated with PTSD status after trait anxiety was controlled for, there was still a trend towards significance, and Fullerton et al. (2001) found that neither prior PTSD, major depression, nor other anxiety disorders could account for the increased PTSD prevalence in females. Finally, Breslau et al. (1997) found that although prior depression and anxiety disorder did reduce the sex difference in PTSD prevalence, they did not eliminate it. Thus, at the present time there is not convincing evidence that sex differences in PTSD can be fully accounted for by negative affectivity/neuroticism and pre-existing symptomatology.
