Furthermore, Dunn et al.'s (1999) longitudinal research on sibling relationships found that both low levels of affection and high levels of hostility between a mother and her partner (usually the father and more often than not a married-partner) were related to later negative behavior directed to the younger sibling by the older sibling, while high levels of reported marital affection was positively linked to the older siblings rating of the younger sibling four years later. In a study of 73 same-sex sibling dyads from two-parent upper- to middle-class families found that negative aspects of the parents' marital relationship were linked to an older siblings' negative behavior towards his or her younger sibling (Erel, Margolin, & John, 1998). Finally, according to cross-sectional research, those mothers out of the 64 families sampled who described their marriages as low in affection were more likely to have children who reported higher levels of conflict and competition between one another (Stocker, Ahmed, & Stall, 1997).