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A vulnerability paradox in the cross-national prevalence of post-traumatic stress disorder

  • Michel L. A. Dückers (a1), Eva Alisic (a2) and Chris R. Brewin (a3)



Determinants of cross-national differences in the prevalence of mental illness are poorly understood.


To test whether national post-traumatic stress disorder (PTSD) rates can be explained by (a) rates of exposure to trauma and (b) countries' overall cultural and socioeconomic vulnerability to adversity.


We collected general population studies on lifetime PTSD and trauma exposure, measured using the WHO Composite International Diagnostic Interview (DSM-IV). PTSD prevalence was identified for 24 countries (86 687 respondents) and exposure for 16 countries (53 038 respondents). PTSD was predicted using exposure and vulnerability data.


PTSD is related positively to exposure but negatively to country vulnerability. Together, exposure, vulnerability and their interaction explain approximately 75% of variance in the national prevalence of PTSD.


Contrary to expectations based on individual risk factors, we identified a paradox whereby greater country vulnerability is associated with a decreased, rather than increased, risk of PTSD for its citizens.

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Corresponding author

Michel Dückers, NIVEL – Netherlands Institute for Health Services Research, Otterstraat 118–124, 3513 CR, Utrecht, The Netherlands. Email:


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Dückers et al. supplementary material
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A vulnerability paradox in the cross-national prevalence of post-traumatic stress disorder

  • Michel L. A. Dückers (a1), Eva Alisic (a2) and Chris R. Brewin (a3)


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A vulnerability paradox in the cross-national prevalence of post-traumatic stress disorder

  • Michel L. A. Dückers (a1), Eva Alisic (a2) and Chris R. Brewin (a3)
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Is there a vulnerability paradox in PTSD? Pitfalls in cross-national comparisons of epidemiological data

Eric Vermetten, Prof Psychiatry, Leiden University Medical Center, The Netherlands
Dan J Stein, Prof and Chair Dept Psychiatry, University of Cape Town, South Africa
Alexander C. McFarlane, Director of the Centre for Traumatic Stress Studies, Professor of Psychiatry, University of Adelaide, Australia
15 August 2016

Dückers et al analyse the relationship between prevalence estimates of trauma exposure and posttraumatic stress disorder (PTSD) in published datasets from 24 countries and a country vulnerability index developed in the 2013 World Risk report. The findings are substantially counter-intuitive; countries with low vulnerability have higher lifetime rates of PTSD, so that countries with low vulnerability and high trauma exposure have the highest rates of lifetime PTSD. The authors do emphasize a number of limitations of their work, and yet they conclude that a “vulnerability paradox” exists for both PTSD and depression, with rates higher in countries with more resources and better health care systems.

This conclusion would seem inconsistent with a great deal of work in global mental health, which emphasizes the considerable treatment gap in mental health services; with under-diagnosis and under-treatment particularly high in low- and middle-income countries (1). It raises the question of what precisely is being measured by epidemiological studies of common mental disorders in general, and by studies of trauma exposure and PTSD in particular (2). There has been no shortage of critics of psychiatric nosology, including the construct of PTSD (3): are counter-intuitive findings such as those of Dückers et al valid in some way, or do they underscore the limitations of our current classification systems, and the epidemiological surveys which employ related measures?

Consider, for example, the findings cited by Dückers et al that in South Africa and Lebanon 73.8% and 68.85 of the population reported exposure to trauma , lower rates than in the Netherlands and Canada. In our view, given the multiple influences that determine self-reported rates of trauma exposure (including those noted by Dückers et al), comparing such rates across surveys is a matter of “comparing oranges and apples”. Other data from other sources may legitimately allow comparison of prevalence estimates: for example, the death rate from motor vehicle accidents in South Africa is 25.1 per 100,000 compared with 3.4 in the Netherlands, and there were 35.7 versus 8.9 murders per 100,000 in South Africa versus the Netherlands (3). Furthermore, rigorous examination of raw data across surveys (which Dückers et al note that they did not undertake), allows valid conclusions about trauma exposure: for example, that a small number of traumatic events account for a larger proportion of all traumatic event exposure across the world (4).

When it comes to PTSD, Dückers et al note a prevalence of PTSD of 0.0% in Nigeria, 3.4% in Lebanon, and 9.2% in Canada; emphasize a range of methodological issues that may have contributed to such findings, but nevertheless proceed to their analysis. In our view, the 0.0% prevalence estimate of PTSD in Nigeria should be considered as a single sampling, prone to any number of measurement errors. While many socio-cultural factors may impact the prevalence of PTSD, given the many universal findings about the phenomenology and psychobiology of PTSD (5), drawing strong inferences from this single data point is not a scientifically sound approach. Again, however, other data and other analytic approaches do allow rigorous conclusions regarding the cross-national epidemiology of PTSD. For example, rigorous analysis of raw data from the World Mental Health Surveys has indicated that dissociative symptoms indicate a particularly severe and impairing subtype of PTSD (6).

In view of these considerations, we wish to express our skepticism about the construct of a “vulnerability paradox”. This is not to criticize all of the fascinating literature on health paradoxes; it may well be the case that well and well-informed populations complain more about health problems than ill but ill-informed populations (7). And it is not to ignore the considerable methodological issues facing psychiatric classification and epidemiology in general, as well as particular issues relevant to trauma such as the causal relationship between trauma exposure and a range of disorders other than PTSD (8). Instead, our argument is that given these issues, certain kinds of analyses (such as those undertaken by Dückers et al) are fundamentally flawed, and the field should instead focus on those analyses which allow rigorous conclusions about trauma exposure and PSTD.

Eric Vermetten, MD, PhD, The Netherlands

Dan J. Stein, MD, PhD, South Africa

Alexander C. McFarlane, MD, PhD, Australia

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(2)Susser E1, Patel al. (2010). Reducing the treatment gap for mental disorders: a WPA survey. World Psychiatry 9(3): 169-176.

(3)Stein, D.J., Seedat, S., Iversen, A., Wessely, S. (2007) Post-traumatic stress disorder: Medicine and politics. Lancet 369:139-144.

(4)World Health Organisation (2016). Monitoring Health for the SDG’s (Sustainable Development Goals),

(5)Benjet, C., et al., (2016). The epidemiology of traumatic event exposure worldwide: results from the World Mental Health Survey Consortium. Psychol Med 46(2): 327-343.

(6)Yehuda, R., et al. (2015). Post-traumatic stress disorder. Nat Rev Dis Primers, 1, 15057. doi: 10.1038/nrdp.2015.57

(7)Stein, D. J., et al. (2013). Dissociation in posttraumatic stress disorder: evidence from the world mental health surveys. Biological Psychiatry, 73(4), 302-312.

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(9)Bryant RA, O'Donnell ML, Creamer M, McFarlane AC, Clark CR, Silove D, The psychiatric sequelae of traumatic injury, American Journal of Psychiatry, 2010;167(3):312-320.

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