Sudden infant death syndrome and the age-cause proxy relationship in infancy.

Evidence from a longitudinal study of the relationship between socioeconomic status and infant mortality in metropolitan Ohio is presented in an effort to throw additional light on the continuing debate over the validity of the age-cause proxy relationship in infancy. The results indicate that while there is a fairly strong and consistent association between neonatal mortality and endogenous causes of death that is little affected by the classification of Sudden Infant Death Syndrome, the nature of the association between postneonatal mortality and exogenous causes of death varies from weak to moderate depending upon where this cause is included. Additional evidence pertaining to the role of SIDS in contributing to the long-standing inverse association between infant mortality and socioeconomic status is presented, thus further emphasizing the need for continued research to clarify the etiologic mechanisms of this poorly understood condition.