Over a six-and-a-half-year period, Colorado surgeons committed tragic errors, according to a new study in the Archives of Surgery (via Health.com). In 25 cases, the wrong patient was taken into surgery. In another 107 incidents, the doctor operated on the wrong part of a patient’s body. Although such unthinkable errors are rare (just .5 percent of all medical mistakes), the numbers, gleaned from a database maintained by a company that provides malpractice insurance to about 6,000 physicians in the state, were “considerably higher” than previously thought. In one example, staff members took the wrong child into an operating room. In another, hospital staffers confused two patients with the same first and last names.

“What is shocking about the data is that each and every one of those wrong-site, wrong-patient errors is really an event that should never happen,” study author Dr. Philip F. Stahel, a visiting associate professor at the University of Colorado School of Medicine in Denver, tells U.S. News & World Report. “These happen much more frequently than we think. This is just the tip of the iceberg.”

And unfortunately, the introduction of much-lauded universal patient protocols—including pre-verification, marking the surgical site, and a “time out” for operating staff before a surgery—have not helped, says Stahel.