A mammogram is a breast x-ray that can detect cancer before it is large enough to feel or cause symptoms. In 2009, the U.S. Preventive Services Task Force (USPSTF), a group of health experts that reviews research and makes recommendations about preventive health care, changed their mammography recommendations to advise that otherwise healthy women have mammography every 2 years beginning at age 50 years. They based this change on calculations that starting annual screening mammography later and getting it less often would cause less harm and be just as safe as starting it earlier and getting it more often. The change in recommendation was controversial because many people believe the benefits of screening mammography outweigh its harms. A study of the benefits and risks of the newer recommendations was needed.