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 ind ependent of the respondent's behaviour. We sought to validate this evaluati on 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 pa st-year personal and network SLEs rated individually, by trained interviewe rs, 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 person al or network independent SLEs. However, familial-environmental factors pla yed an important role in the aetiology of network independent SLEs. For per sonal and network dependent SLEs, by contrast, three of four analyses sugge sted a significant aetiological role for genetic factors with estimated her itabilities ranging from 19 to 51 %. Conclusions. Our results support the validity of interviewer assessments of dependence versus independence of SLEs. As predicted, these assessments we re relatively successful at distinguishing SLEs that were influenced by gen etic factors from those that were not.