The assessment of dependence in the study of stressful life events: validation using a twin design

Background. In the assessment of stressful life events (SLEs), researchers have often tried to evaluate whether individual events are dependent or independent of the respondent's behaviour. We sought to validate this evaluation using a twin methodology. We predicted that dependent SLEs would be more heritable than independent SLEs. Methods. We explored, by twin modelling, the resemblance in two pairs of past-year personal and network SLEs rated individually, by trained interviewers, on a four-point dependence-independence scale. We examined results from two waves of interviews with 785 femal-female twin pairs ascertained from a population based registry. Results. Twin model-fitting found no evidence for genetic effects on personal or network independent SLEs. However, familial-environmental factors played an important role in the aetiology of network independent SLEs. For personal and network dependent SLEs, by contrast, three of four analyses suggested a significant aetiological role for genetic factors with estimated heritabilities ranging from 19 to 51 %. Conclusions. Our results support the validity of interviewer assessments of dependence versus independence of SLEs. As predicted, these assessments were relatively successful at distinguishing SLEs that were influenced by genetic factors from those that were not.