Research participation after terrorism: an open cohort study of survivors and parents after the 2011 Utøya attack in Norway

BACKGROUND: Reliable estimates of treatment needs after terrorism are essential to develop an effective public health response. More knowledge is required on research participation among survivors of terrorism to interpret the results properly and advance disaster research methodology. This article reports factors associated with participation in an open cohort study of survivors of the Utøya youth camp attack and their parents. METHODS: Overall, 490 survivors were invited to two semi-structured interviews that were performed 4–5 and 14–15 months after the attack. The parents of 482 survivors aged 13–32 years were eligible for a complementary study. The study had an open cohort design in which all of the eligible survivors were invited to both waves. Pearson’s Chi squared tests (categorical variables) and independent t tests (continuous variables) were used to compare survivors by participation. RESULTS: Altogether, 355 (72.4 %) survivors participated: 255 in both waves, 70 in wave 1 only, and 30 in wave 2 only. Compared with the two-wave participants, wave-1-only participants were more often non-Norwegian and reported higher exposure, whereas wave-2-only participants reported more posttraumatic stress, anxiety/depression, and somatic symptoms. In total, 331 (68.7 %) survivors had ≥1 participating parents, including 311 (64.5 %) with maternal and 243 (50.4 %) with paternal participation. Parental non-participation was associated with non-Norwegian origin, somatic symptoms and less social support. Additionally, paternal non-participation was associated with having divorced parents, and maternal non-participation was associated with higher age, not living with parents, posttraumatic stress and anxiety/depression symptoms. CONCLUSIONS: Survivors with initial non-participation had more symptoms than did the other participants. Thus, an open cohort design in post-terrorism studies might improve the participation among survivors with higher morbidity. Because the factors associated with maternal and paternal participation differed, it is important to consider potential disparities in the selection of mothers and fathers when interpreting parental data. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13104-016-1873-1) contains supplementary material, which is available to authorized users.