would be fruitless-for preventing schizophrenia because it is not thought to have a causal role. The committee uses the term marker for both biological and psychosocial risk factors of this sort. Incorporated into this definition of risk factor is the concept of vulnerability, which is a predisposition to a specific disease process. Vulnerability traits are identifiable and measurable (and may sometimes be referred to as markers). They are not intrinsically the disease, but they may be necessary for a specific mental disorder to develop. Having vulnerability traits may increase an individual's risk for developing a disorder, but other risk factors also may be necessary for the illness to be expressed.

For years, mental health workers devoted their energies to the study of maladaptation and incompetence (Garmezy, 1983) as attempts were made to identify patterns of functioning in childhood that might portend the future development of mental disorders. Rutter (1985b) described this preoccupation as a “regrettable tendency to focus gloomily on the ills of mankind and all that can and does go wrong. ” But not everyone with risk factors goes on to develop a mental disorder, and the importance of protective factors is becoming more recognized. Recently, research has been directed toward understanding why some children appear to be resilient, and why they come to maturity relatively unscathed by the organic and psychosocial insults that prevent so many of their peers from achieving optimal intellectual, social, and emotional functioning (Werner and Smith, 1992). Werner and Smith (1992) defined resilience as “an unusual or marked capacity to recover from or successfully cope with significant stresses, of both internal and external origin.” Theoretical explanations for the phenomenon of resilience (Rutter, 1985b; Garmezy, 1983) involve the interaction of risk factors, including individual vulnerability, and protective factors to explain why some are spared and others are not. Vulnerable individuals are considered to be those who, by virtue of genetic predisposition, chronic illness, hardship, deprivation, or abuse, are more susceptible to life stressors than others. Thus “they are at risk for failure to master, mature and adapt” (O'Grady and Metz, 1987). Rutter (1985b) defined protective factors as “those factors that modify, ameliorate or alter a person's response to some environmental hazard that predisposes to a maladaptive outcome.” Protective factors seemingly function in a catalytic fashion. They do not necessarily foster normal development in the absence of risk factors, but they may make an appreciable difference on the influence exerted by risk factors. Protective factors also can reside with the individual or the family, community, or institutions and can be biological or psychosocial in nature.

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