Prevalence, Incidence, and Risk Factors for ASD and PTSD

In a previous article, we explored the definition of trauma, and reviewed the DSM-V diagnostic criteria for two trauma-related mental health disorders: acute stress disorder (ASD) and posttraumatic stress disorder (PTSD). The answer to how many people in a given population have AST or PTSD is not straightforward, as it should be considered in the context of how many potentially traumatic events (PTEs) people are exposed to in the general community. Countries in prolonged conflict or who are prone to natural disasters (flooding or hurricanes, for example) may have higher exposure rates to potentially traumatic events and thus a higher per-capita ratio of PTSD in the general population than countries with fewer PTEs occurring. The ratio of PTSD-to-PTE may not be higher, however, than countries with a lower incidence of PTSD per capita, but who have a correspondingly lower exposure to PTEs.

Most people exposed but only 5-10 percent develop PTSD

Large community surveys done in Australia and New Zealand show that 50 to 75 percent of people report at least one PTE in their lives, with most reporting two or more events. The most commonly reported PTEs are having someone close to the individual die unexpectedly (reported by 35 percent of the population), witnessing someone being badly injured or killed (27 percent), or being involved in a life-threatening car accident (13 percent) (Mills, McFarlane, Slade, Creamer, Silove, & Bryant, 2011). Reports of lifetime prevalence of PTSD (that is: the percentage of the population who have had PTSD at some time in their lives) ranges in community samples between 5 and 10 percent.

This means that approximately 15 – 25 percent of people exposed to PTEs have also had a PTSD diagnosis. These figures may be misleading, however, because about 50 percent of the people who develop PTSD recover in the first 12 months regardless of what treatment they have had (or not had) (Kessler, Sonnega, Hughes, & Nelson, 1995). The figures for 12-month prevalence of PTSD (those who have had PTSD in the previous 12 months) are 6.4 percent in Australia and 3.5 percent in the United States (Australian Centre for Posttraumatic Mental Health, 2013a).

Type of PTE is major risk factor

As mental health professionals seeking to assist traumatised clients, we need to know the risk factors for developing ASD and PTSD. An important one is the type of PTE to which the person was exposed. Fortunately, the PTEs associated with the highest rates of PTSD are not always the most commonly occurring PTEs (Mills et al, 2011). Knauss and Schofield reported in the PACFA resource on PTSD (2009) that events with the highest possibility for PTSD to develop for women were rape (44 percent), child sexual abuse (31 percent), and experiencing actual sudden death or threat of sudden death of close associates (27 percent).

Similarly, the Creamer et al study (2001) found that the highest 12-month prevalence of PTSD in Australia was associated with a prior history of rape and molestation, and the lowest was linked to natural disasters and witnessing someone be badly injured or killed; similar findings have been reported in the United States (Australian Centre for Posttraumatic Mental Health, 2013a).

In terms of understanding PTSD among combat veterans, the risk for PTSD seems to vary with the war and/or the country of origin of the soldier. The Kessler et al (1995) survey found that the United States had higher rates of PTSD for its war veterans since the Vietnam War (ranging from 2 – 17 percent, but averaging around 13 percent) than, for instance, Iraq war veterans from the United Kingdom, who averaged 3 – 6 percent (Richardson, Frueh, Acierno, 2010; Hotopf, Hull, Fear, Browne, Horn, Iversen, & Wessely, 2006).

Natural disaster-related rates of PTSD can vary between 4 and 60 percent, with most studies reporting rates under 30 percent. These are often lower than rates for human-made disasters, such as terrorism or technological disasters. Naturally, survivors (at 30-40 percent) and first responders (10 – 20 percent) have higher PTSD rates than the general population (at 5 – 10 percent) (Neria, Nandi, & Galea, 2008).

Pre-trauma risk factors not as powerful in predicting PTSD

Debate has revolved around whether pre- or post-trauma factors influence the occurrence and severity of PTSD. A meta-analysis of 77 studies about risk factors for PTSD found that factors during or after trauma (such as trauma severity, lack of social support, and additional life stressors) had a stronger influence than pre-trauma factors, which were not powerful predictors of PTSD (Brewin, Andrews, & Valentine, 2000). In total, 14 risk factors were identified:

  • Gender
  • Younger age
  • Low socio-economic status
  • Lack of education
  • Lack of intelligence
  • Race
  • Psychiatric history
  • Childhood abuse
  • Previous trauma
  • General childhood adversity
  • Family psychiatric history
  • Trauma severity
  • Lack of social support
  • Life stresses (Brewin et al, 2000)

Dissociation predicts PTSD

One study found that dissociative experiences during a traumatic event were strongly associated with the development of PTSD six months later (Shalev, Peri, Canetti, & Schreiber, 1996). In a meta-analysis of 68 studies, dissociative experiences during or immediately after the traumatic event were the strongest predictor of PTSD out of seven predictors, all of which yielded significant effect sizes: prior trauma, prior psychological adjustment, family history of psychopathology, perceived life threat during the trauma, post-trauma social support, peri-traumatic emotional responses, and peri-traumatic dissociation. Some trauma experts have questioned, however, whether peri-traumatic distress might be related to pre-existing problems in stress tolerance or affect regulation, prior trauma exposure, and/or a tendency to view life events as not controllable (Briere and Scott, 20 06).

The confounding variable of gender

Are women more prone to develop PTSD than men? The answer to this question is not clear. We cited the Brewin et al study above (2000), which identified both gender and prior trauma as risk factors for PTSD. Several studies have shown rape or sexual abuse to be significant predictors of an increased risk to develop PTSD after a traumatic event (Hapke, Schumann, Rumpf, John, & Meyer, 2006; Perkonigg, Storz, & Wittchen, 2000). In a supportive vein, Van der Kolk et al (2005) demonstrated that early trauma exposure, interpersonal trauma, and prolonged trauma were associated with more complex posttraumatic psychopathology. Women experience more traumatic events (i.e., rape and violent assault) and they are more likely to have pre-existing anxiety disorders; these factors may account for their seemingly higher risk for developing PTSD.

However, another study showed that women were at higher risk of developing PTSD than men even when sexual trauma was excluded (Stein, Walker, & Forde, 2000). Similarly, a review article pointed out that women had about twice the risk of developing PTSD even when they experienced the same trauma as men. The most accurate statement that we can make at this stage is that we have neither the research nor the explanatory models about gender differences to understand how they may influence the development of PTSD (Stein et al, 2000).

ASD prevalence not known

Prevalence rates for ASD in the general community are not available in Australia. However, the Australian Centre for Posttraumatic Mental Health (2013a) reports wide variability between different PTEs, including:

  • 9 percent following terrorist attacks
  • 13 – 25 percent following motor vehicle accidents
  • 33 percent for witness to drive-by shootings and
  • 1-14 percent prevalence following traumatic injury (Australian Centre for Posttraumatic Mental Health (2013a).

We reiterate that trauma is a complex issue. While it seems that the type of PTE, the gender of the person exposed to it, and the factors in effect during and after the event have the greatest influence, we must acknowledge that much is yet to be known. What studies agree on at this point is that there are many risk factors and we cannot perfectly predict who will develop ASD or PTSD after an adverse event.

We can, however, remind ourselves about the good news: those who do are only a minority of those exposed to a given incident; most people will bring their coping skills and support systems to bear, prevailing over the event without lasting traumatic stress.

This article was adapted from Mental Health Academy’s upcoming CPD course “Working with Trauma”. This course will describe the therapies which can help you treat patients suffering from trauma.


  • Australian Centre for Posttraumatic Mental Health. (2013a). Australian Guidelines for the Treatment of Acute Stress Disorder and Posttraumatic Stress Disorder. ACPMH, Melbourne, Victoria.
  • Brewin, C. R., Andrews, B., & Valentine, J.D. (2000). Meta-analysis of risk factors for post-traumatic stress disorder in trauma-exposed adults. Journal of Consulting and Clinical Psychology, Vol 68, 748-766.
  • Briere, J. & Scott, C. (2006). Principles of trauma therapy. Guide to symptoms, evaluation, and treatment. Thousand Oaks, CA: Sage Publications.
  • Hapke, U., Schumann, A., Rumpf, H.J., John, U., & Meyer, C. (2006). Post-traumatic stress disorder. The role of trauma, pre-existing psychiatric disorders, and gender. European Archives of Psychiatry and Clinical Neuroscience, Vol 256, 299-306.
  • Hotopf, M., Hull, L., Fear, N.T., Browne, T., Horn, O., Iversen, A., Wessely, S. (2006). The health of UK military personnel who deployed to the 2003 Iraq war; A cohort study. Lancet, Vol 367, No 9524, 1731-1741.
  • Kessler, R.C., Sonnega, A., Hughes, M., & Nelson, C.B. (1995). Posttraumatic stress disorder in the National Comorbidity Survey. Archives of General Psychiatry, Vol 52, No 12, 1048-1060.
  • Mills, K.L., McFarlane, A.C., Slade, T., Creamer, M., Silove, D., Teesson, M., & Bryant. (2011). Assessing the prevalence of trauma exposure in epidemiological surveys. Australian and New Zealand Journal of Psychiatry, Vol 45, No 5, 407-415. DOI: 10.3109/00048674.2010.543654.
  • Neria, Y., Nandi, A., & Galea, S. (2008). Post-traumatic stress disorder following disasters: a systematic review. Psychological Medicine, Vol 38, No 4, 467-480. DOI: 10.1017/S0033291707001353.
  • Perkonigg, A., Kessler, R.C., Storz, S., & Wittchen, J.U. (2000). Traumatic events and post-traumatic stress disorder in the community: Prevalence, risk factors and comorbidity. Acta Psychiatrica Scandinavica, Vol 101, 46-59.
  • Richardson, L.K., Frueh, B.C., & Acierno, R. (2010). Prevalence estimates of combat-related post-traumatic stress disorder: Critical review. Australian and New Zealand Journal of Psychiatry, Vol 44, No 1, 4-19.
  • Shalev, A.Y., Canetti, L., & Schreiber, S. (1996). Predictors of PTSD in injured trauma survivors: A prospective study. American Journal of Psychiatry, Vol 153, 219-225.
  • Stein, M.B., Walker, J.R., & Forde, D.R. (2000). Gender differences in susceptibility to posttraumatic stress disorder. Behaviour Research and therapy, Vol 38, 619-628.