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Increased Incidence Rate of Trauma- and Stressor-related Disorders in Denmark After the Breivik Attacks in Norway

Hansen, Bertel T.a,b; Dinesen, Peter T.a; Østergaard, Søren D.c,d

doi: 10.1097/EDE.0000000000000705
Descriptive Epidemiology

Background: On 22 July 2011, Anders Breivik killed 77 adults and children in Norway. Having recently documented increases in the incidence of trauma- and stressor-related disorders in Denmark after the 9/11 attacks, we hypothesized that the Breivik attacks—due to their geographic proximity—would be followed by even larger increases in Denmark.

Methods: Using population-based data from the Danish Psychiatric Central Research Register (1995–2012), we conducted an intervention analysis of the change in the incidence of trauma- and stressor-related disorders after the Breivik attacks.

Results: The incidence rate increased by 16% over the following 1½ years after the Breivik attacks, corresponding to 2736 additional cases. In comparison, 9/11 was followed by a 4% increase. We also present evidence of a subsequent surge in incidence stimulated by media attention.

Conclusion: This study bolsters previous findings on extra-national consequences of terrorism and indicates that geographic proximity and media coverage may exacerbate effects.

From the aDepartment of Political Science, University of Copenhagen, Copenhagen, Denmark; bDepartment of Political Science, Stanford University, Stanford, CA; cDepartment of Clinical Medicine, Aarhus University, Aarhus, Denmark; and dPsychosis Research Unit, Aarhus University Hospital, Risskov, Denmark.

Submitted December 23, 2016; accepted June 27, 2017.

This work was support by grants 2011_01_0609 and CF14-0703 from the Carlsberg Foundation. S.D.Ø. was supported by grant R165-2013–15320 from the Lundbeck Foundation. The funders had no influence on the following: design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

The authors report no conflicts of interest.

Availability of data and code for replication: Data and code for replication are available in eAppendix 2 and eAppendix 3, respectively.

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Correspondence: Søren D. Østergaard, Psychosis Research Unit, Department of Clinical Medicine, Aarhus University Hospital, Skovagervej 2, 8240 Risskov, Denmark. E-mail:

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