There are 48.4 million uninsured Americans — about 18 percent of the population — according to the last Census. But who are they? And what is the best way to get them signed up for new health insurance coverage options that roll out this fall? The U.S. Centers for Medicare and Medicaid Services has just released a brief for those with a stake in getting people signed up, including insurers, consumer advocates and state officials. The analysis breaks the uninsured down by age, race, geography and "lifestyle and psychographic segments" (that's marketing-speak for people who share some of the same demographic profile).