Violent crime is one of the most detrimental factors affecting the quality of life in many industrialized countries, and most persons incarcerated due to violent offenses have committed previous offenses (Hamparin, Schuster, Dinstz, & Conrad, 1978; Lindqvist, 1986; Tracy, Wolfgang, & Figlio, 1990; Vankeinhoitolaitos, 1997). The majority of all violent crime is attributable to a relatively small population exhibiting recidivistic violent behavior (Hamparin et al., 1978; Tracy et al., 1990). It is remarkable how little systematic and controlled scientific research has focused on the mental disorders underlying habitual violent behavior: The first studies on the quantitative risk assessment of recidivistic violent behavior were only published in the 1990s.

Several practical difficulties have hindered research on violent behavior. Many violent offenses are mild and are even not registered in police records. This obstacle can be avoided by focusing only on the most serious crimes, such as homicide. Even this does not help to improve the coverage of the offenders completely, since in many industrialized countries a large proportion of homicides remains unsolved (e.g., about 30% in the United States, International Criminal Police Organisation, 1991). It is difficult to obtain comprehensive groups of recidivistic offenders for research purposes in countries with high crime rates caused by extensive use of illicit drugs, a high incidence of organized crime, and gun violence. This is probably because higher crime rates mean lower crime clearance rates.