Emily Oster evaluated data behind many of the accepted rules of pregnancy. (Should you drink caffeine? Is sushi OK?) She says most advice given to moms-to-be is wrong. More recently, she's been studying how grocery store purchases change once a person has been diagnosed with a health challenge like diabetes. Household scanner data "helps us look at people outside of a monitored health setting, and really see in the real world what are the changes people make, what changes are impossible to make, and who is able to change a lot," she says.