While we do cancer clinical trials to test drugs, exposures that increase risks are found with observational studies. These have also been instrumental in highlighting disparities. Tim Rebbeck and Rafa Irizarry discuss the challenges these studies pose. Timothy Rebbeck, PhD is the Vincent L. Gregory, Jr. Professor of Cancer Prevention at the Harvard TH Chan School of Public Health and Professor of Medical Oncology at the Dana-Farber Cancer Institute. Dr. Rebbeck’s research focuses on the etiology and prevention of cancer, with an emphasis on cancers with a genetic etiology and those that are associated with disparities in incidence or mortality by race. He has directed multiple large molecular epidemiologic studies and international consortia that have been used to identify and characterize genes involved in cancer etiology, understand the relationship of allelic variation with biochemical or physiological traits, explore interactions of inherited and somatic genomic variation with epidemiological risk factors. Our Data Science Zoominars feature interactive conversation with data science experts and a Q+A session moderated by Rafael A. Irizarry, PhD, Chair, Department of Data Science at Dana-Farber Cancer Institute.