Bullying Perpetration and Depressive Symptoms: A Causal Investigation of TwinLife Data

Bullying perpetration has been associated with depressive symptoms. Although the bullying literature is large, most studies are correlational and cannot address the question of causation directly. This study explored bidirectional causal relationships between bullying perpetration and depressive symptoms using data from the TwinLife study, a comprehensive longitudinal survey of German twins. We aimed to clarify whether bullying perpetration leads to depressive symptoms or vice versa, or if other underlying factors might explain their co-occurrence.

The analysis included 1975 twin pairs from the TwinLife study, with data on depressive symptoms and bullying. The analysis used an extension to the Direction of Causation model, a bivariate causal inferential twin model that adjusts the effect of measurement error. A range of models was tested. Age, sex, inter-twin aggression and household income were included in all models as covariates.

After testing five models with and without causal paths, we found the model without causal paths but including common genetic and unique environmental liabilities best explained the data.

It was found that depressive symptoms and bullying perpetration share genetic influences.