Final answer:
Research on sibling rivalry supports the statement that destructive sibling conflict in middle childhood is associated with negative outcomes, including anxiety and depressed mood.
Step-by-step explanation:
Research on sibling rivalry supports statement 3) Destructive sibling conflict in middle childhood is associated with negative outcomes, including anxiety and depressed mood. Studies have shown that siblings may engage in conflict and competition, which can lead to emotional distress and negative psychological effects. It is important for parents to intervene and promote positive sibling relationships to minimize the negative outcomes of sibling rivalry.