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EFFECTS OF EXPOSURE ON PREVALENCE AND CUMULATIVE RELATIVE RISK: DIRECT AND INDIRECT EFFECTS IN A RECURSIVE HAZARD MODEL
Authors:Lawrence L. Wu  Steven P. Martin
Affiliation:New York University;
University of Maryland, College Park
Abstract:This paper outlines decomposition methods for assessing how exposure affects prevalence and cumulative relative risk. Let     x     denote a vector of exogenous covariates and suppose that a single dimension of time   t   governs two event processes     T 1  and   T 2.    If the occurrence of the event     T 1    determines entry into the risk of the event     T 2,    then subgroup variation in     T 1    will affect the prevalence     T 2,    even if subgroups in the population are otherwise identical. Although researchers often acknowledge this phenomenon, the literature has not provided procedures to assess the magnitude of an exposure effect of     T 1    on the prevalence of     T 2.    We derive decompositions that assess how variation in exposure generated by direct and indirect effects of the covariates     x     affect measures of absolute and relative prevalence of     T 2.    We employ a parametric but highly flexible specification for baseline hazard for the     T 1  and   T 2    processes and use the resulting parametric proportional hazard model to illustrate the direct and indirect effects of family structure when     T 1    is age at first sexual intercourse and     T 2    is age at a premarital first birth for data on a cohort of non-hispanic white U.S. women.
Keywords:
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