Absolute deterrent effects. Effects that are demonstrated when an intervention produces better outcomes compared to no treatment.

Age of onset (of serious violence). The age at which an individual reports his or her first act of serious violence.

Age-specific prevalence. The proportion of youths at any given age who report having committed at least one serious violent act in the past year.

Aggravated assault. An unlawful attack by one person upon another wherein the offender uses a weapon or displays it in a threatening manner, or the victim suffers obvious severe or aggravated bodily injury involving apparent broken bones, loss of teeth, possible internal injury, severe laceration, or loss of consciousness. Along with homicide, robbery, and rape, one of the four violent crimes covered in this report.^*

Aggression (aggressive behavior). Behavior, physical or verbal, that is intended to harm another person.

Antisocial attitudes. Favorable attitudes toward violence, dishonesty, and rule breaking with hostility toward authority.

Antisocial behaviors. Problem behaviors that range from relatively minor acts such as lying, stealing, truancy, disobedience, and temper tantrums to serious nonviolent or violent behavior such as burglary or aggravated assault.

Attention-deficit/hyperactivity disorder (ADHD). A cognitive disorder characterized by restlessness, excessive activity, and difficulty paying attention.

Career length. Variously defined as the number of years of active offending; or the maximum number of consecutive years of offending; or the span between the first and last year during which a youth meets the criteria for a serious violent offender.

Case study research. A type of study design involving multiple observations of a single individual over time.

Chronic offenders. Variously defined by some minimum number of offenses; for example, youths with three or more serious violent offenses per year.

Contagion effect (of violence). Unproved notion that seeing or hearing about violence in news coverage encourages violent or aggressive behavior.

Control group. A group that receives standard care or no intervention in a research study, compared to the experimental, treatment, or intervention group.

Co-occurrence (of problem behaviors). The simultaneous display of violence and other problem behaviors (e.g., substance use, property crimes, gun ownership). Although these behaviors occur together, it cannot be assumed that one behavior causes another.

Conduct disorder. Childhood disorder marked by persistent acts of aggressive or antisocial behavior.

Cross-sectional research. A type of study design, frequently used in public opinion polls, surveys, and epidemiological research. It involves a single contact with participants for data collection at a given point in time and thus does not permit researchers to estimate individual-level change, development, or predictive effects of a given risk or protective factor on later violent behavior.

Cumulative prevalence (lifetime prevalence or ever-prevalence). The proportion of youths at any particular age who have ever committed a serious violent offense.

Delinquent (antisocial) lifestyle. A pattern of consciously chosen and sustained behaviors that include antisocial or illegal acts, typically involving property crimes, substance use, gun ownership, and promiscuity.

Deterrent effects (absolute). See Absolute deterrent effects.

Deterrent effects (marginal). See Marginal deterrent effects.

Developmental perspective (on youth violence). An approach to understanding youth violence that considers the complex interaction of individuals with their environment at particular times in their lives; this approach recognizes that patterns of behavior change over the life course.

Developmental trajectory (course, pathway, or progression) of violent behavior. The distinct pattern of violent behavior that emerges for an individual over time.

Does Not Work program. Prevention programs in this category demonstrate consistent evidence of no effects or harmful effects.

Early-onset trajectory. A pattern of violent behavior that emerges before adolescence, defined in this report as about age 13. In this pathway, problem behaviors in childhood gradually escalate over time to more violent ones, culminating in serious violence before adolescence. This pattern is less prevalent than the late-onset trajectory and is characterized by higher offending rates, greater seriousness of adolescent offenses, and greater persistence of violence from adolescence into adulthood.

Effect size. The predictive power of an individual or general type of risk or protective factor; or the size of the deterrent effect of an intervention compared to no treatment or a standard treatment. The measure used for risk factor effect sizes in this report is a simple correlation between two variables. For program effectiveness, the effect size measure is the average difference (standardized) between the treatment and control group means on the selected recidivism measure.

Effectiveness trials. Research that tests for benefits to participants in a natural or applied setting.

Efficacy trials. Research that tests for benefits to participants in a controlled or experimental setting.

Epidemiology. Study of the factors influencing the incidence, frequency, and distribution of health-related events in the population; identifying appropriate risk and protective factors for prevention and intervention programs.

Experimental research. A type of study design involving comparison of a group that receives an intervention (experimental or treatment group) and a group that receives standard care or no intervention (control group) in which participants are randomly assigned to one of these groups. This study design permits researchers to assess cause-and-effect relationships and can be used to determine intervention effectiveness.

Externalizing symptoms. A behavioral pattern characterized by the acting out of psychological problems.

Hazard rate. The proportion of individuals who initiate a given behavior (e.g., serious violence) at a given age.

Homicide. The willful (nonnegligent) killing of one human being by another; along with robbery, aggravated assault, and rape, one of the four violent crimes covered in this report.*

Iatrogenic. In the context of youth violence, interventions that are harmful or actually increase involvement in violence.

Incident rate. The number of self-reported violent acts within a given-sized population, a measure of the volume of violence; as used in this report, the number of violent acts per 1,000 young people.

Intervention. See Secondary prevention.

Late-onset trajectory. A pattern of violent behavior that emerges in adolescence, defined in this report as about age 13. This pattern is more prevalent than the early-onset trajectory and is characterized by a shorter period of involvement, lower frequency of offending, and a lower likelihood of continuing into adulthood. Individuals who are characterized by this pattern typically give few external signs in childhood that they will become violent offenders.

Level of control. Efforts to take into account other factors that might influence the data or responses from participants in a research study; contributes to the quality of a given study.

Level of evidence. The strength of the evidence amassed for any scientific fact or conclusion.

Lifestyle. A pattern of consciously chosen, observable behaviors that a person engages in on a consistent and regular basis.

Locally representative (probability) sample. In this report, the term representative sample is used to refer to a probability sample—a sample that is selected in such a way that its characteristics can be generalized to the population (e.g., city or county) from which it was drawn with a known degree of accuracy. The accuracy of generalizations from probability samples is given in the form of a confidence interval. In this report, 95 percent confidence intervals (CIs) are reported, indicating an upper and lower bound for the population estimate that is accurate at least 95 percent of the time.

Longitudinal research. Used in etiological (causal) and developmental research, a type of study design involving multiple contacts with the same study participants over time; allows researchers to estimate how well a given risk or protective factor predicts later violent behavior for individuals or groups.

Marginal deterrent effects. Effects that are demonstrated when an intervention produces significantly better outcomes compared to another treatment; may underestimate the true effects of the intervention compared to receiving no treatment at all.

Maturation effect. An effect associated with growing older or maturing, it may refer to changes in one’s physical or social development. The term refers specifically to a sharp reduction in youth violence observed during the transition to adulthood, usually during the late teen years to age 20.

Mediating-effects analysis. An analysis that permits researchers to determine whether a change in the targeted risk or protective factor accounts for an observed change in violence.

Meta-analysis. A rigorous statistical method of combining the results of several studies to obtain more reliable estimates of the effects of a general type of treatment or intervention; can be used to summarize program evaluation and draw overall conclusions about the strength and consistency of the influence, or effect size, that particular types of programs have on violence.

Model program. A prevention program that meets the highest scientific standard for effectiveness, as evidenced in published evaluations; has a significant, sustained preventive or deterrent effect and has been replicated in different communities or settings. It has been shown to work and can be expected to have a positive result in a wide range of community settings.

Monitoring the Future (MTF). A cross-sectional survey of high school seniors that obtains self-reports about a wide range of social attitudes and behaviors, including drug use and violence. This study has been conducted annually since 1975 by the University of Michigan’s Institute for Social Research and is the longest-running national survey of its type. It also has a longitudinal component, following high school seniors into their adult years, but little has been published on the longitudinal data.

National Crime Victimization Survey (NCVS). A national, self-report, household survey conducted by the Bureau of Justice Statistics that provides annual estimates of levels and rates of criminal victimization in the United States. Residents of selected households age 12 and older are interviewed about their victimization experiences, including serious violent assaults, rapes, and robberies and whether they reported these crimes to law enforcement officials.

National Electronic Injury Surveillance System (NEISS). Operated by the U.S. Consumer Product Safety Commission since 1992, the system monitors types of injuries treated in emergency departments, including those related to firearms.

National Television Violence Survey (NTVS). A recent content analysis of television programming examining its portrayal of violence. The study assessed a total of 2,500 hours of television programming during the 1994 through 1997 viewing seasons.

National Youth Survey (NYS). A national, longitudinal study of U.S. youths age 11 to 17 begun in 1976. Study participants have been interviewed nine times, with the last interviews completed in 1993. The study includes both self-reported and official police records. Measures of a wide range of delinquent, violent, and drug-using behaviors, as well as conventional behaviors, are obtained in confidential interviews.

Nationally representative sample. A probability sample of a country, such as the United States or the United Kingdom. A sample drawn in such a way that its characteristics can be generalized to the U.S. population with a known degree of accuracy (confidence interval). See Locally representative sample.

Personality disorders. Behavior syndromes characterized by maladaptive personality patterns that result in chronically dysfunctional perceptions, thoughts, and behaviors.

Physical aggressiveness. Relatively nonserious forms of violent behavior, often displayed in early childhood and continued into adolescence, including hitting, biting, kicking, punching, or otherwise intentionally hurting others.

Population-based studies. Studies based on general population samples rather than selected or institutional samples (e.g., prisoners, hospital patients, nursing home residents, expelled students). Findings from these studies apply to general populations, whereas findings from studies of selected or institutional samples apply specifically to persons in these settings or groups.

Post-traumatic stress disorder (PTSD). Disorder in which a stressful experience is traumatic and produces severe, recurring symptoms.

Prevalence rate. As used in this report, the proportion of youths involved in one or more violent behaviors during some specified time interval, for example, the past year, by age 18, or ever.

Primary prevention (true prevention). As defined in this report, strategies and programs that reduce the likelihood that youths will initiate violent behavior compared to youths in a control group; programs designed to target youths who have not yet become involved in violence or encountered specific risk factors for violence; identifies behavioral, environmental, and biological risk factors associated with violence and takes steps to educate individuals and communities about and protect them from these risks.

Probability sample. A sample selected in such a way that its characteristics can be generalized to the population from which it was drawn with a known degree of accuracy. The level of accuracy for proportions, means, and correlations is presented as a 95 percent confidence interval, which contains the true population value 95 percent of the time. See Locally representative sample.

Promising program. Prevention programs in this category meet two of the scientific standards for effectiveness; they do not meet all of the rigorous standards of Model programs, but they are recognized and encouraged with the caution that they be carefully evaluated.

Protective factor. As used in this report, personal characteristics or environmental conditions that reduce the potential harmful effect of a risk factor for violent behavior; characteristics that buffer or moderate the effect of risk. Protective factors are grouped into individual, family, school, peer group, and community domains.

Public health approach. A practical, goal-oriented, and community-based approach to promoting and sustaining health. This approach seeks to identify risk and protective factors, determine when in the life course they typically occur and how they operate, and enable researchers to design preventive programs that are effective in reducing risk and promoting protection.

Quasi-experimental research. A type of study design with experimental and control groups but without random assignment to these groups. Groups are matched on selected characteristics, or differences are controlled in the analysis. The claim of group equivalence or comparability is not as strong with this design as in an experimental design.

Rape (forcible rape). The carnal knowledge of a person, forcibly and/or against that person’s will; or not forcibly or against the person’s will where the victim is incapable of giving consent because of his or her temporary or permanent mental or physical incapacity (or because of his or her youth). Along with homicide, robbery, and aggravated assault, one of the four violent crimes covered in this report.^*

Reliability (of research instruments or measures). The consistency of a measure; the measure yields the same result on different occasions or applications (when no real change has occurred).

Replication. Repeating an intervention or prevention program at multiple sites to determine if the results will be the same; establishes that a program can be effective at other sites when implemented by new teams under different conditions.

Risk factor. In the context of youth violence, personal characteristics or environmental conditions that increase the likelihood that a young person will become violent but that may not actually cause a person to become violent. Risk factors are grouped into individual, family, school, peer group, and community domains. The more risk factors a young person is exposed to, the greater the likelihood that he or she will become violent.

Risk marker. A personal characteristic or environmental condition associated with known risk factors but having no causal relation to violence on its own.

Robbery. The taking or attempting to take anything of value from the care, custody, or control of a person or persons by force or threat of force or violence and/or putting the victim in fear. Along with homicide, aggravated assault, and rape, one of the four violent crimes covered in this report.*

Sampling. The selection of persons to be studied in a research project.

Schizophrenia-spectrum disorders. Broad category of disorders that includes individuals with symptoms such as serious distortions of reality (including hallucinations and delusions), withdrawal from social interaction, and disorganization and fragmentation of perception, thought, and emotion, for which other plausible explanations could be ruled out.

Secondary prevention. In the context of this report, strategies and programs that reduce the risk of violence among youths who display one or more risk factors for violence (high-risk youths).

Self-directed violence. Self-inflicted injury and suicide; not the focus of this report.

Self-report studies. Research that asks people in confidence to describe their own behavior. In the context of youth violence, surveys that ask young people in confidence about violent acts they have committed or have been victims of during a given period of time.

Serious violent crime (serious violence or index crimes). As defined in this report, aggravated assault, robbery, rape, and homicide.

Serious violent youths. Youths involved in serious violent behavior (crimes). They are typically high-frequency offenders who are involved in both serious and nonserious offenses. These youths account for a major share of all criminal behavior by persons under age 18.

Socially disorganized community. A community characterized by high levels of poverty, unemployment, high turnover of residents, and a large proportion of disrupted or single-parent families.

Socioeconomic status. In reference to youths, their parents’ education, occupation, and income.

Statistical significance. The level of confidence with which one can conclude that a difference between two or more groups (generally a treatment and control group) is the result of the treatment delivered rather than the selection process or chance. A probability value of .05 is widely accepted as the threshold for statistical significance in the social and behavioral sciences; a probability value below this threshold (p < .05) indicates that a difference of this magnitude could happen by chance less than 5 percent of the time.

Superpredators. A new breed of violent youths who commit more frequent and vicious violent crimes, without remorse, than in previous generations. Contrary to a recent myth, there is no evidence that this type of violent youths emerged in the 1990s.

Surveillance. A type of research that establishes the nature of a health problem, describes its incidence and prevalence trends, and monitors its magnitude over time. Public health specialists use this information to determine appropriate prevention and intervention efforts.

Sustained effects. Changes in individual competencies and environmental conditions produced by effective programs that last at least a year beyond treatment or participation in the intervention.

Tertiary prevention. In the context of this report, strategies and programs that prevent further violence or the escalation of violence among youths already involved in violent behavior.

Uniform Crime Reporting (UCR) program. Operated by the FBI since the 1930s, the program monitors arrests made by law enforcement agencies across the United States and compiles annual arrest information.

Validity (of research instruments or measures). The degree to which an instrument tests what it is supposed to test, or a measure assesses what it is supposed to assess.

Wraparound services. An approach that is designed to tailor social services to the individual.

Youth Risk Behavior Survey (YRBS). A national school-based survey conducted biannually by the Centers for Disease Control and Prevention in collaboration with Federal, state, and private-sector partners since 1990. The survey monitors six important health behaviors, including those that may result in violent injuries among both public and private school students in grades 9 to 12. The survey is voluntary, is anonymous, provides for parental consent for minors, and oversamples minorities.