a1 From the Department of Sociology, Bedford College, University of London
a2 Institute of Psychiatry, University of London
Methods are first described for testing for and measuring the proportion involved in the causal link between life-events and psychiatric disorders; the paper then deals with the nature of the causal effect itself. A method is described (and developed mathematically in an appendix) which enables a choice to be made between a triggering effect in which events are seen as precipitating an illness that would probably have occurred before long for other reasons, and a formative effect in which life-events either substantially advance onset in time, or bring it about altogether. The method is used to demonstrate the presence of a formative effect in depressive and a triggering effect in schizophrenic disorders.
1 The work on schizophrenia and depression has been supported by the Foundation Fund for Research in Psychiatry, the Medical Research Council, and the Social Science Research Council.