Much research relating to children and death has focused on the age-graded developmental model originally proposed by Nagy in the late 1940s. Children are alleged to pass from an infantile to a mature view, seeing death first as separation, then as the result of intervention by a supernatural being, and finally as an irreversible biological process. Accepted theory for thirty years, scholars have since noted difficulty in duplicating Nagy's findings and have come to question the universal application of the developmental model. Bluebond-Langner proposes an alternative model in which all views of death are present in all stages of development. She maintains that the particular orientation a child displays is a result of personal and social experiences.