Project Summary In the project, "Constructing, Validating, and Testing the Predictive Power of Life-Course Health Histories," we will create a comprehensive guide to help researchers discern whether and when they can use retrospective health data from nationally representative surveys to create lifetime health histories. Our project leverages enormous investments the scientific community has made to measure population and individual health on cross-sectional and longitudinal surveys. We will use data from four major surveys to create life histories for each survey respondent for 11 acute or chronic health conditions. We will then validate the constructed health histories, comparing the prevalence of the condition for a given birth cohort in a past year against contemporaneously measured prevalence rates for the same condition, demographic group and in the same calendar year. We will develop our guide and data with attention to three major factors that cause researchers to hesitate about using retrospective questions to generate life health-histories – recall bias, similarities and differences in sampling rules and sample characteristics, and selective mortality. Our overall aims are to conduct a “proof-of-concept” exercise to explore whether and for what conditions one can use retrospective questions to generate life health histories and to provide a guide for researchers to use. Our work products will expand the set of questions researchers can address with retrospective health data already collected on existing surveys. Our results will enable researchers to describe and study the etiology of a wide range of health conditions that are currently difficult to study because of sample size limitations.