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§  Jenkins and Smith (1991) examined three aspects of poor marital relationships which were frequency and severity of angry arguments, disagreement over child-rearing issues, and periods of silent tension. They found that it was frequency and severity of angry arguments that were associated with an increase in children's disorders. Open and severe quarrelling was also related to more parenting problems, such as monitoring children less, and being overly critical of them. 

Kindling hypothesis - Kendler et al (2000) examined the findings of four interviews over nine years with female twin pairs. It was found that the first episode of depression was frequently caused by a severe life event. However, for further episodes of depression the relation with adversity was not noticeable. The same authors (Kendler et al., 2001) then studied genetic factors. It was found the kindling effect was more noticeable for those with low genetic risk. However, those with a high genetic risk frequently experienced a first depression without a severe life event. Therefore, there are two routes to experiencing depression in the absence of severe life stressors. The first is high genetic risk. The second is the experience of prior episodes of depression in a life of considerable adversity.