Since 1999, medical research teams have been studying statistics concerning wrong-site surgeries. This information includes facts about wrong-patient and wrong-procedure treatments, consequences of surgical errors and preventative actions taken. However, reporting the events is voluntary, so the total number of wrong-site surgeries reported may be far lower than the actual occurrences.
There are a number of reasons why hospitals report medical mistakes. For one, it is often required by law, but it also helps to keep hospitals and doctors aware of the number of errors they are making. Reporting can also serve as a way to shame doctors into paying more attention so that they don't make surgical errors.