Republican presidential candidate Sen. John McCain waits backstage before the presidential debate with Obama in 2008. Scott Olson/AP hide caption

itoggle caption Scott Olson/AP

President Barack Obama and Republican presidential candidate Mitt Romney both campaigned in the battleground state of Ohio this week. AP hide caption

itoggle caption AP

Families in a predominantly Latino youth soccer league gather for matches in Aurora. Hispanics make up nearly a third of the city's population, according to the 2010 Census. Megan Verlee for NPR hide caption

itoggle caption Megan Verlee for NPR

There's no industry standard size for food and drink portions, so it's hard to compare a Big Gulp with a McDonald's medium soda. Joe Raedle/Getty Images hide caption

itoggle caption Joe Raedle/Getty Images

Traders work in the bond pit at the Chicago Board of Trade in 1995. In recent decades, much of the trading has left the pits and gone electronic. Michael S. Green/AP hide caption

itoggle caption Michael S. Green/AP

President Obama greets supporters during a campaign rally on Saturday in Milwaukee. Scott Olson/Getty Images hide caption

itoggle caption Scott Olson/Getty Images

Republican presidential candidate Mitt Romney speaks at a campaign event at the Cox Pavilion Friday in Las Vegas. David Becker/Getty Images hide caption

itoggle caption David Becker/Getty Images

Arefa with her host family, sisters Jami Valentine (left) and Staci Freeman. Doctors in the U.S. have been treating Arefa's third-degree burns, and also performed skin-graft surgery for the top of her head. Each morning still requires a fresh dressing. Gloria Hillard for NPR hide caption

itoggle caption Gloria Hillard for NPR

Mitt Romney takes the stage at a campaign rally at the Military Aviation Museum in Virginia Beach, Va., on Sept. 8. Brian Snyder/Reuters/Landov hide caption

itoggle caption Brian Snyder/Reuters/Landov

An incentive system that gave bonuses to teachers upfront, with the threat of having to give the money back if student performance didn't improve, proved effective in one study. David Franklin/iStockphoto.com hide caption

itoggle caption David Franklin/iStockphoto.com

Canned food is a source of BPA exposure, but researchers aren't sure whether it causes childhood obesity. Above, the soup isle at a grocery store in Washington, D.C. Maggie Starbard/NPR hide caption

itoggle caption Maggie Starbard/NPR

The Michigan Gala apples on this packing line will soon be in short supply. After a mild fall and winter, then a late-April freeze, Michigan's apple cultivation has dropped 90 percent. Noah Adams/NPR hide caption

itoggle caption Noah Adams/NPR