A perceived discrepancy in parental treatment has a negative effect on sibling relationships. Observational research by Stocker et al. (1990) found that excessive maternal control directed toward older sibling, as rated by an independent coder, leads to a sibling relationship rated as both competitive and controlling. Their study also showed similar results for excessive maternal control directed toward the younger sibling. For those mother-sibling-sibling triads that were rated as having a mother who directed attention toward the younger sibling, the sibling relationship was also rated as competitive and controlling while being witnessed during a video-taped session. According to the results of research by Brody et al. (1987), families in which mothers are differentially controlling, responsive, or affectionate toward their children are more likely to have siblings who report relationships high in conflict and low in friendliness. Finally, while researching mostly white, middle-class families, McHale and Pawletko (1992) found that, among the 62 adolescent sampled (half of which had a younger sibling who was physically disabled), perceived differential treatment of siblings was negatively related to sibling relationship quality.