Read the following short passages and choose the best answers to the questions that follow each passage.
Therapists have just completed an extensive study of recently delinquent juveniles in order to determine which factors contributed most to the delinquency. The researchers found that in a great majority of the cases of delinquency, the parents met, on average, fewer than 4 times per week with their children. From this data, the therapists have determined that a failure to spend time together with the children is a major factor leading to delinquency.
Which one of the following, if true, would cast the most doubt on the researcher's hypothesis ?