Associations Between Lone Motherhood and Depression: A Co-twin Control Study

Abstract

Prior research has documented an association between lone motherhood and depression using traditional analysis tools. Such an association, however, is insufficient for establishing a causal effect. There are many possible non-causal confounds of this association, including a shared genetic background, or a shared influence by the same socioeconomic factors. We introduce a useful approach for studying behavioural data, and one that has never been used in the study of lone motherhood: twin research. Twin research is useful for the investigation of non-experimental associations because it allows observed associations to be decomposed into between-pair (lone motherhood associated with depression across pairs) and within-pair (the member of discordant pairs who is a lone mother is also more depressed). We then use this method to examine whether the relation between lone parenthood and depression is causal, or the result of genetic and shared environmental confounds. The study uses the Swedish Twin Registry, the largest twin dataset in the world. Our results show that even when controlling for genetic and shared-environmental confounds, there is still a significant association between lone motherhood and depression. Finally, we present conclusions and recommendations based on our results in the context of existing public policies.