Chapter 4
Risk Factors for Youth Violence

Research has documented the magnitude of youth violence and the trends in that violence over time. But what do we know about why young people become involved in violence? Why do some youths get caught up in violence while others do not? There is no simple answer to these questions, but scientists have identified a number of things that put children and adolescents at risk of violent behavior and some things that seem to protect them from the effects of risk.

INTRODUCTION TO RISK AND PROTECTIVE FACTORS

The concepts of risk and protection are integral to public health. A risk factor is anything that increases the probability that a person will suffer harm. A protective factor is something that decreases the potential harmful effect of a risk factor. In the context of this report, risk factors increase the probability that a young person will become violent, while protective factors buffer the young person against those risks. The public health approach to youth violence involves identifying risk and protective factors, determining how they work, making the public aware of these findings, and designing programs to prevent or stop the violence.

Risk factors for violence are not static. Their predictive value changes depending on when they occur in a young person's development, in what social context, and under what circumstances. Risk factors may be found in the individual, the environment, or the individual's ability to respond to the demands or requirements of the environment. Some factors come into play during childhood or even earlier, whereas others do not appear until adolescence. Some involve the family, others the neighborhood, the school, or the peer group. Some become less important as a person matures, while others persist throughout the life span. To complicate the picture even further, some factors may constitute risks during one stage of development but not another. Finally, the factors that predict the onset of violence are not necessarily the same as those that predict the continuation or cessation of violence.

Violence prevention and intervention efforts hinge on identifying risk and protective factors and determining when in the course of development they emerge. To be effective, such efforts must be appropriate to a youth's stage of development. A program that is effective in childhood may be ineffective in adolescence and vice versa. Moreover, the risk and protective factors targeted by violence prevention programs may be different from those targeted by intervention programs, which are designed to prevent the reoccurrence of violence.

This report groups risk and protective factors into five domains: individual, family, peer group, school, and community, which includes both the neighborhood and the larger society (Box 4-1). Factors do not always fit neatly into these areas, however. Broken homes are classified as a family risk factor, but the presence of many such families in a community can contribute to social disorganization, an important community-level risk factor (Bursik & Grasmick, 1993; Elliott et al., 1996; Sampson & Lauritsen, 1994).

Risk Factors

Risk factors are not necessarily causes. Researchers identify risk factors for youth violence by tracking the development of children and adolescents over the first two decades of life and measuring how frequently particular personal characteristics and social conditions at a given age are linked to violence at later stages of the life course. Evidence for these characteristics and social conditions must go beyond simple empirical relationships, however. To be considered risk factors, they must have both a theoretical rationale and a demonstrated ability to predict violence—essential conditions for a causal relationship (Earls, 1994; Kraemer et al., 1997; Thornberry, 1998). The reason risk factors are not considered causes is that, in most cases, scientists lack experimental evidence that changing a risk factor produces changes in the onset or rate of violence.

Box 4-1: Early and late risk factors for violence at age 15 to 18 and proposed protective factors, by domain

As used in this report, risk factors are personal characteristics or environmental conditions that predict the onset, continuity, or escalation of violence.

The question of causality has practical implications for prevention efforts. Prevention depends largely on risk factors being true causes of violence. In practical terms, research has amassed enough strong, consistent evidence for the risk factors discussed in this report to provide a basis for prevention programs, even though a strict cause-and-effect relationship has been established for relatively few of them.

Most of the risk factors identified do not appear to have a strong biological basis. Instead, it is theorized, they result from social learning or the combination of social learning and biological processes. This means that violent youths who have violent parents are far more likely to have modeled their behavior on their parents’ behavior—to have learned violent behavior from them—than simply to have inherited it from them. Likewise, society’s differing expectations of boys and girls—expecting boys to be more aggressive, for example—can result in learned behaviors that increase or decrease the risk of violence.

The bulk of the research that has been done on risk factors identifies and measures their predictive value separately, without taking into account the influence of other risk factors. More important than any individual factor, however, is the accumulation of risk factors. Risk factors usually exist in clusters, not in isolation. Children who are abused or neglected, for example, tend to be in poor families with single parents living in disadvantaged neighborhoods beset with violence, drug use, and crime. Studies of multiple risk factors have found that they have independent, additive effects—that is, the more risk factors a child is exposed to, the greater the likelihood that he or she will become violent. One study, for example, has found that a 10-year-old exposed to 6 or more risk factors is 10 times as likely to be violent by age 18 as a 10-year-old exposed to only one factor (Herrenkohl et al., 2000).

Researchers have theorized that risk factors also interact with each other, but to date they have found little evidence of interaction. What evidence does exist suggests that interactions between or among factors produce only small effects, but work in this area is continuing. To date, much more research has been done on risk factors than protective factors, but that picture, too, is changing.

Developmental Progression to Violence
Scientific theory and research take two different approaches to how youth violence develops—one that focuses on the onset of violent behavior and its frequency, patterns, and continuity over the life course and one that focuses on the emergence of risk factors at different stages of the life course. Chapter 3 describes two developmental trajectories for the onset of violent behavior—one in which violence begins in childhood (before puberty) and continues into adolescence, and one in which violence begins in adolescence.

In contrast, this chapter considers the timing of risk factors. It identifies the individual characteristics, experiences, and environmental conditions in childhood or adolescence that predict involvement in violent behavior in late adolescence—that is, age 15 to 18, the peak years of offending. Research shows that different risk factors may emerge in these two developmental periods and that the same risk factors may have different effect sizes, or predictive power, in these periods.

The timing of risk factors and the onset of violence are connected. Only risk factors that emerge in early childhood can logically account for violence that begins before puberty. However, these early risk factors may or may not be implicated in violence that begins in adolescence. In fact, studies show that many youths with late-onset violence did not encounter the childhood risk factors responsible for early-onset violence. For these youths, risk factors for violence emerged in adolescence (Huizinga et al., 1995; Moffitt et al., 1996; Patterson & Yoerger, 1997; Simons et al., 1994).

Table 4-1 lists early and late risk factors and estimates their effect sizes for violence at age 15 to 18. It does not distinguish between youths who became violent before puberty and those who first became violent in adolescence; both groups are included among youths who were violent in late adolescence. However, the table does indicate that different risk factors emerge before puberty (age 6 to 11) and after puberty (age 12 to 14) and that the same risk factors have different effect sizes in these periods. Thus, for example, the table shows that substance use in childhood has a greater effect on violence at age 15 to 18 than parental abuse or neglect does and that substance use in childhood has a greater effect on violence than substance use in early adolescence. (The table is discussed at greater length below, in A Note on Sources.)

Table 4-1. Effect sizes of early and late risk factors for violence* at age 15 to 18

Limitations of Risk Factors
Risk factors are powerful tools for identifying and locating populations and individuals with a high potential for becoming violent, and they provide valuable targets for programs aimed at preventing or reducing violence. But there are important limitations to our knowledge about and use of risk factors.

The following cautions are worth bearing in mind:

• No single risk factor or set of risk factors is powerful enough to predict with certainty that youths will become violent. Poor performance in school is a risk factor, for example, but by no means will all young people who perform poorly in school become violent. Similarly, many youths are exposed to multiple risks yet avoid becoming involved in violence (Garmezy, 1985; Rutter, 1985; Werner & Smith, 1982, 1992).
• Because public health research is based on observations and statistical probabilities in large populations, risk factors can be used to predict violence in groups with particular characteristics or environmental conditions but not in individuals.
• Given these two limitations, assessments designed to target individual youths for intervention programs must be used with great care. Most individual youths identified by existing risk factors for violence, even youths facing accumulated risks, never become violent (Farrington, 1997; Huizinga et al., 1995; Lipsey & Derzon, 1998).
• Some risk factors are not amenable to change and therefore are not good targets for intervention (Earls, 1994; Hawkins et al., 1998a). Being born male is an example.
• Of the risk factors that are amenable to change, some are not realistic targets of preventive efforts. Eliminating poverty is not a realistic short-term goal, for example, but programs that counter some of the effects of poverty are. (Eliminating or reducing poverty should be a high-priority long-term goal, however.)
• Some situations and conditions that influence the likelihood of violence or the form it takes may not be identified by longitudinal studies as risk factors (predictors) for violence. Situational factors such as bullying, taunting, and demeaning interactions can serve as catalysts for unplanned violence. The social context can influence the seriousness or form of violence—for example, the presence of a gun or a gathering crowd of peers that makes a youth feel he (or she) needs to protect his (or her) reputation. These may not be primary causes of violence, yet they are contributing factors and are important to understanding how a violent exchange unfolds. Such influences, although important, may not be identified in this report because of the way risk factors are defined.
• Many studies of risk factors, particularly earlier ones, drew their samples from white boys and young men. The limited focus of these studies calls into question their predictive power for girls and women and for other racial or ethnic groups. Differences among cultures and their socialization and expectations of girls and boys may modify the influences of some risk factors in these groups.

Nonetheless, most of the risk factors identified in this report do apply broadly to all young people. All children go through the same basic stages of human development—and prevention of youth violence is based on understanding when and how risk factors come into play at various stages of development. Moreover, there is some evidence that most risk factors are equally valid predictors of delinquency and violence regardless of sex, race, or ethnicity (Rosay et al., 2000; Williams et al., 1999). Sophisticated studies that identify how cultural differences affect the interplay of the individual and his or her surroundings will make possible more effective prevention efforts.

Protective Factors

There is some disagreement about exactly what protective factors are. They have been viewed both as the absence of risk and as something conceptually distinct from risk (Guerra, 1998; Jessor et al., 1995; Reiss & Roth, 1993; Wasserman & Miller, 1998). The former view typically places risk and protective factors on the opposite ends of a continuum. For example, good parent-child relations might be considered a protective factor because it is the opposite of poor parent-child relations, a known risk factor. But a simple linear relationship of this sort (where the risk of violence decreases as parent-child relations improve) blurs the distinction between risk and protection, making them essentially the same thing.¹

The view that protection is conceptually distinct from risk (the view used in this report) defines protective factors as characteristics or conditions that interact with risk factors to reduce their influence on violent behavior (Garmezy, 1985; Rutter, 1985; Stattin & Magnusson, 1996). For example, low family socioeconomic status is a risk factor for violence, and a warm, supportive relationship with a parent may be a protective factor. The warm relationship does not improve the child’s economic status, but it does buffer the child from some of the adverse effects of poverty. Protective factors may or may not have a direct effect on violence (compare Jessor et al., 1995 and Stattin & Magnusson, 1996).

Interest in protective factors emerged from research in the field of developmental psychopathology. Investigators observed that children with exposure to multiple risk factors often escaped their impact. This led to a search for the characteristics or conditions that might confer resilience—that is, factors that moderate or buffer the effects of risk (Davis, 1999; Garmezy, 1985; Rutter, 1987; Werner, 1989). Protective factors offer an explanation for why children and adolescents who face the same degree of risk may be affected differently.

The concept of protective factors is familiar in public health. Wearing seat belts, for example, reduces the risk of serious injury or death in a car crash. Identifying and measuring the effects of protective factors is a new area of violence research, and information about these factors is limited. Because they buffer the effect of risk factors, protective factors are an important tool in violence prevention.

Like risk factors, proposed protective factors are grouped into individual, family, school, peer group, and community categories. They may differ at various stages of development, they may interact, and they may exert cumulative effects (Catalano et al., 1998; Furstenberg et al., 1999; Garmezy, 1985; Jessor et al., 1995; Rutter, 1979; Sameroff et al., 1993; Thornberry et al., 1995). Just as risk factors do not necessarily cause an individual child or young person to become violent, protective factors do not guarantee that an individual child or young person will not become violent. They reduce the probability that groups of young people facing a risk factor or factors will become involved in violence.

A Note on Sources

This chapter draws heavily on four important studies: Lipsey & Derzon’s meta-analysis of 34 longitudinal studies on risk factors for violence (1998); Hawkins et al.’s study of malleable risk and protective factors drawn from 30 longitudinal studies, including some not included in the Lipsey & Derzon meta-analysis (Hawkins et al., 1998c); Paik and Comstock’s meta-analysis of 217 studies of exposure to media violence and its effects on aggression and violence (1994); and the National Institute of Mental Health’s Taking Stock report (Hann & Borek, in press), an extensive review of research on risk factors for aggression and other behavior problems.

Table 4-1 is adapted from the tables presented in the Lipsey and Derzon and Hawkins et al. meta-analyses. The risk factors in Table 4-1 predict felonies—that is, violent and property crimes—at ages 15 to 18, the peak years of involvement.² Entries in bold are effect sizes from the meta-analyses by Lipsey and Derzon, Hawkins et al., and Paik and Comstock for various classes of risk factors; other entries are effect sizes reported in two or more longitudinal studies. (Risk classes are described in Appendix 4–A and later sections of this chapter.) Some of the risk classes in Table 4-1 include several separate risk factors. For example, psychological condition includes hyperactivity, daring, and attention problems.

Additional risk factors and classes of risk factors have been added from other sources. For example, there is adequate evidence to establish harsh, lax, or inconsistent discipline as a separate risk factor, although Lipsey and Derzon include it in the poor parent-child relations class. Academic failure, family conflict, and belonging to a gang are additional examples of risk factors not included in any of the meta-analyses.

The measure of effect size used in these tables is a bivariate correlation (r), or simple correlation between two variables. All estimates of effect size are statistically significant and are based on multiple studies, with those for risk classes typically involving more studies than those for separate risk factors. The studies reviewed in Lipsey and Derzon, Paik and Comstock, and Hawkins et al. are not cited here; however, other studies that were used to establish a risk factor or that are included in estimates of effect size are cited.³

There is a rich and extensive body of research on risks for antisocial behavior, externalizing behavior, conduct disorder, and aggression (Hann & Borek, in press). Each of these terms defines a pattern or set of behaviors that includes aggressive or violent behavior, but most of the behaviors included are either nonphysical, nonviolent acts or relatively minor forms of physical aggression. Risk factors for antisocial behavior may be quite different from those that predict violent behavior (robbery, aggravated assault, rape, and homicide). Since antisocial behavior does not present the potential for serious injury or death that violence does, this report relies on studies that identify risk factors for serious offenses generally and violent behavior specifically, bearing in mind that the vast majority of serious offenders report having been involved in violent offenses.

Summary

Risk and protective factors can be found in every area of a child or adolescent’s life, they exert different effects at different stages of development, and they gain strength in numbers. The public health approach to the problem of youth violence 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 to be put in place at just the right time to be most effective.

This chapter describes what is known about individual, family, school, peer group, and community risk and protective factors that exert their effects in childhood and adolescence. It describes the power of early risk factors, which come into play before puberty, and late risk factors, which exert their influence after puberty, to predict the likelihood of youth violence.

Footnotes