The flag of the state of Arizona flies at half-staff outside University Medical Center in Tucson, Ariz., on Jan. 8. Chris Morrison/AP hide caption

itoggle caption Chris Morrison/AP

Natasha Smahlei, a model, works at the Caitlin Raymond International Registry exhibit in October during the New England Business Expo at the DCU Center in Worcester, Mass. Paul Kapteyn/Courtesy of www.telegram.com hide caption

itoggle caption Paul Kapteyn/Courtesy of www.telegram.com

Natasha Smahlei, a model, works at the Caitlin Raymond International Registry exhibit in October during the New England Business Expo at the DCU Center in Worcester, Mass. Paul Kapteyn/Courtesy of www.telegram.com hide caption

itoggle caption Paul Kapteyn/Courtesy of www.telegram.com

In Oxford, England, people are 16 times more likely to get a particular kind of hip replacement than residents of London. Wikimedia Commons hide caption

itoggle caption Wikimedia Commons