New study -93 % of adverse events went unreported

You need to read the full report. http://oig.hhs.gov/oei/ reports/oei-06-08-00221.pdf

reviewed hospitals did not generate incident reports for 93 percent of the events, including some of the most serious events involving death or permanent disability to the patient.  The lack of such reports could prevent hospitals from tracking events as required by Federal regulation and suggests that hospital incident-reporting systems may be an unreliable source of information for Patient Safety Organizations (PSO), entities that aggregate and analyze hospital data about events.