According to the U.S. National Center for Education Statistics, school violence is a serious problem. In 2007, the latest year for which comprehensive data were available, a nationwide survey, conducted biennially by the Centers for Disease Control and Prevention (CDC) and involving representative samples of U.S. high school students, found that 5.9% of students carried a weapon (e.g. gun, knife, etc.) on school property during the 30 days antedating the survey. The rate was three times higher among males than among females. In the 12 months antedating the survey, 7.8% of high school students reported having been threatened or injured with a weapon on school property at least once, with the prevalence rate among males twice that as among females. In the 12 months antedating the survey, 12.