Structural equation modelling was used to perform the statistical analyses on questionnaire data collected from 1556 twin and non-twin siblings.
Poor sleep quality was more strongly associated with dependent as compared to independent negative life events (r = .34 and .15, respectively). There was substantial overlap in the genetic influences on the association between dependent negative life events and poor sleep quality (rA = .62[.43–.81]), suggesting gene–environment correlation. Environmental overlap was small (rE = .16[.04–.28]). Genetic influences accounted for a large proportion of the association (70 % [.47–.92]) with the remaining co-variance due to non-shared environment (30 % [.08–.53]). Genetic liability to sleep quality was not moderated by dependent negative life events.
Genetic and environmental effects on sleep are not necessarily distinct but to some extent work in concert. This should be considered in future studies assessing the genetic and environmental effects on sleep.