Most contemporary investigators accept the notion that the origins of schizophrenia are best understood within a vulnerability-stress model (Zubin & Spring, 1977). Persons are vulnerable to the disorder on the basis of genetic predisposition and prenatal and postnatal integrity. This vulnerability can be modified by stressful life events occurring throughout life. If life events have a negative effect on subsequent development, they are said to enhance the risk for this disorder. On the other hand, if the probability of subsequent disorder is reduced by certain life events, these events are said to be protective.

If the concept of a protective factor is to be meaningful, then it must be other than the inverse of a risk factor. In order to establish a protective role for life events, at any point in development, one must be able to document that the previously established expectancy of disorder has been reduced. This implies that we have robust vulnerability markers for schizophrenia that permit this type of analysis, a doubtful situation at the present time. In fact, the very existence of this volume indicates the interest in summarizing the current state of knowledge with regard to risk and protective factors so as to point the way to the next generation of studies in this area.

Because we lack clear-cut vulnerability markers for schizophrenia that can be applied to individuals early in their lives to estimate their risk for the disorder, does this mean that we are unable to investigate the other side of the equation regarding stressful life events?