Risk Factors & Vulnerability
Epidemiologic and developmental researchers have introduced the notion of risk factors to identify variables known to predict later disorder. A risk factor is defined by its probabilistic relation to an outcome variable, without implying determinism, early onset of disorder, or inevitability of outcome. Risk factors are either markers of some other causal process or causal factors themselves. One goal of developmental research is to determine the causal status of risk markers. As noted earlier in this chapter, social competence, or level of adaptive functioning, is a broad risk factor for many disorders, but empirical research must determine whether this factor merely indicates risk that is caused by some other factor (eg, genes) or constitutes a contributing factor in itself.
Risk factors often accumulate in enhancing the likelihood of eventual disorder. For example, the probability of conduct disorder is enhanced by low socioeconomic status, harsh parenting, parental criminality, marital conflict, family size, and academic failure. The number of factors present seems to be a stronger predictor of later disorder than is the presence of any single factor, suggesting that causal processes are heterogeneous and that risk factors cumulatively increase vulnerability to a causal process.
The concept of vulnerability has been applied to individuals who are characterized by a risk factor. Many empirical studies of the development of disorder use samples that are defined by a risk factor (such as offspring of alcoholics and first-time juvenile offenders); however, it is not clear that the causal and developmental factors are similar in disordered individuals who come from high-risk and low-risk populations.