By too many measures, America is a lot less healthy than a developed nation has any business being. But just how sick -- or just how well -- are we? Broad national averages are limited things -- very good at telling you the what, but notoriously bad at telling you much more. Who are the one-third of Americans who don't have a weight problem, and how can the rest of us become like them? Why do some of us get our cancer screenings and make sure our kids are vaccinated while others don't? It's hard enough to get a thorough profile of any one person's health outlook. Now imagine putting 300 million of us on the examining table together. That's where TIME's inaugural national health checkup can help.