The 1975 study involved 2,143 families nationwide, and the 1985 study focused on 6,002 families. The 1985 study used only 4,032 families in its comparison with the 1975 study, since the 1975 sample included only children aged 3 to 17 and excluded single-parent families. Data were collected with the conflict-tactic scale, which consists of a list of options people can use in a conflict with another family member. The physical aggression measured involves pushing, grabbing, shoving, slapping, throwing things, kicking, fighting, punching, hitting with an object, beating, and threatening with a knife or gun. Almost 16 percent of American couples experienced at least one violent incident; the rate of severe violence was 6.1 percent. A total of 6,900,000 children were severely assaulted by their parents. There tended to be more violence in families where husbands claimed to be the head of the household. There was a substantial reduction in the rates of family violence from 1975 to 1985, both in child abuse and in spouse abuse. Since the early 1970's, structured efforts to intervene in family violence have increased significantly, as evidenced in the increase in child protective service workers and family therapy and marriage counseling.