Developmental psychologists are trying to evaluate different explanations for the effects of poor parenting on behavior problems in children. One important scientific thinking principle that the psychologists should keep in mind is to?

rule out rival hypotheses using additional research

Explanation:

A rival hypothesis is an explanation of an effect which is not what the researcher first hypothesized. Developmental psychology deals with studying the psychological changes a person goes through in the span of their lifetime. This includes childhood and adulthood.

When a child is being studied for behavioral problems a wrong explanation for the behavior may lead to a remedy that may be in fact harmful for the mental development of the child.

Hence, any rival hypotheses must be ruled out.