the rate at which violent persons commit violent acts (the number of violent acts committed by a person each year);
the persistence (or duration) of violent persons' histories of committing violent acts (e.g., length in years from the commission of the first act of violence to the last act of violence); and
the seriousness (or harmfulness) of the violent acts committed by individuals (e.g., extent of physical harm inflicted).
Our review seeks to transcend the particular foci of the source studies (which typically concentrate on particular types of victims or forms of injury, such as spouse abuse or rape) and instead summarizes commonalities in the methods and findings of studies about violence. Considerable empirical evidence suggests that violent people frequently engage in a range of violent and other types of antisocial acts. Children who throw heavy or sharp objects at their parents are likely to hit their siblings or peers and to lie, set fires, and be truant from school (Lewis and Balla, 1976); prison inmates who are ''violent predators" (they committed robbery and assault and dealt drugs prior to incarceration) are just as likely to have an arrest history including rape as are fellow inmates who are actually serving time for rape (Chaiken and Chaiken, 1982, and unpublished analysis of the same data). Thus, a focus on a narrow range of violent acts would fail to identify what is commonly perceived as violence.
Furthermore, the characteristics of victims and the forms of injury are less important for classification and prediction than are characteristics and past behavior of individuals. Although any behavioral outcome is dependent on an individual's response to the environment, including his or her access to specific classes of victims, certain biological, psychological, and social characteristics of individuals dramatically increase or decrease the probability that they will engage in specific forms of behavior, independent of environmental factors. This concept has been supported by such studies as Glaser (1964), Hare (1979), Irwin (1970), Mann et al. (1976), McCord and McCord (1959), and Robins and Wish (1977), and has guided our thinking in this review.
To carry out the review, it was useful to distinguish between classification and prediction, even in situations where this distinction is unclear in the source document. The following section explains the basis for this distinction and summarizes those methodological issues that classification and prediction have in common; it also contains a brief summary of the correlates of violence. In the following section, we turn attention to classification. There we review the purposes of classification, types of