Study protocol: The association between workplace bullying and suicidal behaviour: A register-based prospective study of 98,330 participants in Denmark.

Aim: To present a protocol for the analysis of the prospective association between workplace bullying and suicidal behaviour. Method: The analyses will be carried out on a sample of 98,330 participants (64% women, n=62,582) taken from a pooled dataset of nine Danish questionnaire-based surveys (2004-2014) including self-reported measures of workplace bullying. The pooled dataset is linked to national register-based data on suicidal behaviour. We will fit multivariate Cox proportional hazard models to estimate Hazard Ratios (HR) and their 95% confidence intervals for the association between baseline workplace bullying and subsequent suicidal behaviour of any type (suicide attempt and death by suicide combined), adjusting for sex, age, living status, socio-economic status and previous history of psychiatric morbidity. We will have an 80% chance of detecting a hazard ratio of 1.67 for suicidal behaviour of any type, a hazard ratio of 1.74 for suicide attempt, and a hazard ratio of 2.54 for death by suicide. Results: The study results will be reported in an English-language manuscript to be submitted to peer-reviewed research journals. Conclusion: The data available for this study are adequate to examine the prospective associations between workplace bullying and suicidal behaviour of any type (suicide attempt and death by suicide combined). The purpose of this protocol is to reduce risk of data-driven findings.