In 1977, two psychologists named Joseph Zubin and Bonnie Spring came up with a model that they believed could explain why some people develop schizophrenia. The model was based on the interaction between two key variables present in every person: biological vulnerability and environmental stressors. Although the model was initially developed to explain schizophrenia, it has since been used to analyze the development of a wide range of mental disorders. It is not popular with all psychologists, however.
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