Epidemiologists are the watchful guardians of public health. They collect and analyze data to track the status quo. When there are deviations, they crunch the numbers to understand who is getting sick, where, how, and why. Dr. Meredith Shiels is an epidemiologist and senior investigator at the National Cancer Institute (NCI) studying cancer mortality rates to discern what populations might be at higher risk, figure out ways to mitigate those risks, and evaluate whether those measures are working.