Trauma exposure

Our estimate of people who had experienced at least one lifetime serious event (86%) appears to be higher than similar estimates in the World Mental Health Survey.^{Reference Benjet, Bromet, Karam, Kessler, McLaughlin and Ruscio20} That survey included data from other Western European countries such as Belgium, the Netherlands, Germany, France, Italy, Spain, Portugal and Northern Ireland (54%–73%), as well as Israel (75%), Australia (76%), New Zealand (79%) and the United States (83%). Our estimate is at the highest level also when compared with other studies from Australia (75%),^{Reference Chapman, Mills, Slade, McFarlane, Bryant and Creamer21} Canada (76%)^{Reference Van Ameringen, Mancini, Patterson and Boyle22} and Sweden (81%),^{Reference Frans, Rimmö, Åberg and Fredrikson23} or another study from the Netherlands (81%).^{Reference De Vries and Olff24}

Variation in the different estimates may result from different measurement methods and how the different types of life events were presented. Compared with our use of a 17-event questionnaire, the World Mental Health Survey covered 27 potentially traumatic events from the Composite International Diagnostic Interview. Studies from Australia, Canada, Sweden and the Netherlands asked about 29, 18, 7 and 36 events or types of events, respectively. However, all studies included an open-ended question about serious events not specified, and based on face value, the different methods seemed to extract roughly the same information about lifetime traumatic events.

According to the World Bank national accounts data,²⁵ Norwegians and some other populations with the highest numbers of reported serious life events, such as the Swedish and Dutch, are among the wealthiest in the world. Also, for other measurements of personal and social well-being, these populations are in the forefront. For example, Norway topped the global happiness rankings for 2017, with Sweden and the Netherlands among the top 10 countries.^{Reference Helliwell, Layard and Sachs26} Of note, people in these countries report higher numbers of serious life events than people in many countries with less social and economic progress, such as Bulgaria (29%),^{Reference Benjet, Bromet, Karam, Kessler, McLaughlin and Ruscio20} Romania (42%)^{Reference Benjet, Bromet, Karam, Kessler, McLaughlin and Ruscio20,Reference Florescu, Mihaescu-Pintia, Ciutan, Sasu and Gălăon27} and Mexico (69%),^{Reference Benjet, Bromet, Karam, Kessler, McLaughlin and Ruscio20,Reference Borges, Benjet, Petukhova and Medina-Mora28} or even a war-exposed population in Lebanon (69%).^{Reference Karam, Mneimneh, Dimassi, Fayyad, Karam and Nasser29}

Some countries with much lower economic welfare than Norway also have a high incidence of serious life events, such as Colombia, Peru and Ukraine (83%–85%).^{Reference Benjet, Bromet, Karam, Kessler, McLaughlin and Ruscio20} However, we were unable to find examples of countries with a higher incidence of reported serious life events than Norway, despite huge differences in welfare, social distress and conflicts.

Higher numbers of reported serious life events in the Norwegian population can represent a high risk of exposure, or more likely, there are significant differences in what people in various countries remember or consider to be a serious life event. Remarkable individual differences in severity perception have been documented in the literature, even among people who have experienced the same event.^{Reference Heir, Blix and Knatten30} Also, the severity perception of an event often changes over time,^{Reference Giosan, Malta, Jayasinghe, Spielman and Difede31,Reference Heir, Piatigorsky and Weisæth32} which can affect what people report in retrospect. Social or cultural influences can lead to adjustments in perception. For example, our 48.5% prevalence of lifetime exposure to life-threatening illness or injury is remarkably higher than the overall 11.8% prevalence of lifetime exposure to life-threatening illness or injury in the World Mental Health Survey.^{Reference Benjet, Bromet, Karam, Kessler, McLaughlin and Ruscio20} Yet there are no indications that there is more disease or injury in the Norwegian population. Hypothetically, people living in a society with low expectations of adverse life events may be more likely to perceive or remember certain experiences as serious.

Systematic differences may also occur in the likelihood of underreporting some traumas because the experiences are embarrassing or otherwise culturally sensitive.^{Reference Schaeffer, Stone, Turkkan, Bachrach, Jobe, Kurtzman and Cain33} However, for reports of sexual assaults, the numbers are quite stable among countries. The finding that 1.7% of men and 10.1% of women had been subjected to sexual assault was close to the 1.1% male and 9.4% female rape prevalence reported in another Norwegian study.^{Reference Thoresen, Myhre, Wentzel-Larsen, Aakvaag and Hjemdal34} These values are also similar to those in other Scandinavian studies in which 9% of women in Denmark^{Reference Balvig and Kyvsgaard35} and 11% of women in Sweden³⁶ reported lifetime rape or attempted rape. Quite similarly, 11% of women in a study that included 28 European countries had been subjected to sexual assault.³⁷

Current PTSD

Comparisons of our point prevalence of PTSD with other studies are challenging because most studies to date have focused on lifetime prevalence. The point prevalence is a joint function of lifetime prevalence and duration of the disorder. Because about half of PTSD cases remit within 6 months and the probability of remission does not vary much across exposure types,^{Reference Morina, Wicherts, Lobbrecht and Priebe38} the point prevalence of PTSD is expected to be considerably lower than lifetime prevalence estimates. Still, the point prevalence in our study is higher than lifetime PTSD reported from various populations in Germany, Belgium, France, Spain, Italy, Bulgaria, Romania, Ukraine, Brazil, Columbia, Mexico, Japan, China, South Korea, Lebanon, Iraq and South Africa.^{Reference Dückers, Alisic and Brewin3} Only countries like Sweden,^{Reference Frans, Rimmö, Åberg and Fredrikson23} the Netherlands,^{Reference De Vries and Olff24} Australia,^{Reference Chapman, Mills, Slade, McFarlane, Bryant and Creamer21} New Zealand^{Reference Oakley-Browne, Wells, Scott, Kessler and Ustun39} and the United States^{Reference Kessler, Berglund, Demler, Jin, Merikangas and Walters40} have lifetime PTSD prevalence rates that are equal to or higher than the point prevalence in the Norwegian population. Thus, even when considering that estimates of lifetime prevalence may be conservative because of recall bias,^{Reference Belli, Perfect and Lindsay41} it is striking that the point prevalence in the Norwegian population is higher than a broad range of lifetime estimates of other countries, ranking Norway among the world's top countries for PTSD.

The high PTSD rate in the Norwegian population supports the ‘vulnerability paradox’ in which those living in countries with more resources have higher, rather than lower, PTSD risk.^{Reference Dückers, Alisic and Brewin3} Essential for PTSD is the exposure to actual or threatened death, serious injury or sexual violence.¹ The subjective perception of life threat, however, can play a key role in the development and maintenance of PTSD regardless of the objectively estimated threat of the actual exposure.^{Reference Heir, Blix and Knatten30} Social and cultural factors can affect what is perceived as threatening or violating. Again, people living in a society with low expectations of adverse life events may be more likely to perceive an adverse event as serious. Indeed, moderation of negative appraisals of the traumatic event or its sequelae is an appropriate approach in cognitive therapy of PTSD.^{Reference Ehlers and Clark42} At the population level, high attention to serious life events and their potential harm to mental health outcomes may have the opposite effect.

According to general principles, in situations where many people are exposed to some risk,^{Reference Rose43,Reference Rose44} a small shift in the distribution of perceived threat may have a large effect on the number of people with PTSD. Thus, small between-population differences in threat appraisals can lead to paradoxical results in the cross-population prevalence of PTSD.

Another approach to PTSD is the ‘centrality of the event’, which refers to how central an event is to a person's life story and identity.^{Reference Rubin, Berntsen and Bohni45} The perceived centrality of stressful events is consistently associated with higher levels of post-traumatic stress symptoms.^{Reference Berntsen and Rubin46–Reference Blix, Birkeland, Solberg, Hansen and Heir48} According to Rubin et al,^{Reference Rubin, Berntsen and Bohni45} the memory of the traumatic event and its centrality are key elements in the development and maintenance of trauma symptoms. Consequently, societies in which an adverse event is more easily constructed as central in people's life story and identity might have higher rates of PTSD. Compared with most other countries, Norwegian society pays high attention to serious life events and the possibility of adverse health outcomes.^{Reference Shultz, Thoresen and Galea49,Reference Kristensen, Dyregrov, Weisæth, Straume, Dyregrov and Heir50} Faced with the high rates of PTSD in the general population, it is appropriate to question whether this level of attention can have negative effects on mental health at the population level.

The high rates of trauma exposure and PTSD compared with other countries should also be discussed as a possibility of underreporting in other countries and stigma of mental illness being greater. An openness culture about mental health problems has occurred in Norway in recent decades. This has helped to remove some stigma around mental disorders and caused more people to recognise or report such problems. On the other hand, it may also have made it easier to blame an illness or event that can cause illness, rather than taking personal responsibility for life's difficulties.

Methodological considerations

Interpreting the results of this study requires noting some limitations. First, we had a moderate (36%) response rate. Responders and non-responders did not differ significantly in gender or age, and the distributions of persons living in rural and urban areas were similar. Also, the responders were considered representative of the general Norwegian population in terms of education, employment and relationship status.^{Reference Schou-Bredal, Heir, Skogstad, Bonsaksen, Lerdal and Grimholt11,Reference Bonsaksen, Grimholt, Skogstad, Lerdal, Ekeberg and Heir12} Nevertheless, we cannot exclude the possibility of sampling bias. For instance, our findings could be biased if people affected by trauma found the study more relevant and were more willing to complete the survey; in contrast, there also could be bias if they found the study too personal or emotionally disturbing and avoided responding to trauma questions.^{Reference Hussain, Weisæth and Heir51}

Second, we used the PCL-5 self-reported measure to assess the prevalence of PTSD, rather than using clinical assessment. When compared with the Structural Clinical Interview of the DSM-IV, a Norwegian version of the PCL is almost equivalent in its ability to assess PTSD in epidemiological research.^{Reference Hem, Hussain, Wentzel-Larsen and Heir52} Nevertheless, the lack of clinical interviews in the present study involves a limitation with unknown direction of the possible bias.

Third, we did not assess comorbid psychological conditions. Depression and anxiety disorders are clinically important when considering the long-term mental health effects of trauma exposure.^{Reference Hussain, Weisæth and Heir53} Some symptoms included in a PTSD diagnosis, such as difficulty sleeping or concentrating, could be part of depression or other psychiatric disorders and thus bias the prevalence rates of PTSD.

Finally, retrospective reports of serious life events can be associated with recall bias. Some events could have been forgotten or were no longer considered important, whereas others could have been subject to memory amplification.^{Reference van Giezen, Arensman, Spinhoven and Wolters54} Moreover, as with all diagnostics of PTSD, the attribution of symptoms to a particular event is a subjective appraisal.

Strengths of the study include the national probability sample, trauma questionnaires that were embedded in a wider health research context and not presented solely as a trauma survey, use of point prevalence rather than lifetime prevalence of PTSD and a responder population apparently representative of the general Norwegian population.

Clinical implications

High estimates of serious life events and correspondingly high rates of PTSD support the vulnerability paradox in which people in wealthy countries with more resources and better healthcare services have a higher risk of PTSD. A possible explanation may be that high expectations for a risk-free life or a happy life can lead to a low threshold for perceiving adverse events as life-threatening or as violating integrity. High attention to various life events and their potential harm to mental health can make such events more central in people's life stories and identities, contributing to adverse health effects such as PTSD.

Most people experience some potentially traumatic events during their lives, so a small shift in the perception of life threat or violation of integrity can greatly affect the number of people with PTSD. The suggested explanations for the high rates of PTSD in the Norwegian population should be regarded as hypotheses. More research is needed to determine how different aspects of a society can affect people's experiences of serious life events. Yet there is reason enough to consider the Hippocratic principle of not doing harm. Health professionals should be aware of possible harmful effects of promoting people's perception of life threat or violation of integrity.