Scientists have been studying the effects of lead in children’s blood, bones, and tissue for a number of years. It is known that lead reduces intelligence and can cause a variety of other problems. A study directed by Dr. Herman Needleman, a psychiatrist at the University of Pittsburgh Medical Center, examined some of these problems. Two hundred boys attending public schools in Pittsburgh were recruited. Each boy was categorized as having low or high levels of lead in their bones. Each boy was then assessed by his teachers on a 4-point scale (where 1 = low, 2 = moderate, 3 = high, and 4 = extreme) on degrees of aggression. Is there evidence to infer that boys with high levels of lead are more aggressive than boys with low levels of lead?