Fifty Percent of Adverse Events Are Preventable

Most medical errors are related to defects in the health care delivery system, not individual negligence or misconduct, and, therefore, have the potential to be significantly reduced through system redesign or transformation.

An adverse event is defined as “an unintended injury or complication resulting in death, disability or prolonged hospital stay caused by healthcare management.”

Fifty percent of adverse events, i.e. one in every two events, can be prevented. Studies – see the references below – have shown that 37–70% of adverse events are preventable. For the sake of simplicity, I have summarized the study results to one figure – 50%.


  1. Baker GR, Norton PG, Flintoft V, Blais R, Brown A, Cox J, et al. The Canadian Adverse Events Study: the incidence of adverse events among hospital patients in Canada. CMAJ 2004;170(11):1678–86. doi:10.1503/cmaj.1040498

  2. Schiöler T, Lipczak H, Pedersen BL et al. Forekomsten af utilsigtede hændelser pa˚ sygehus. En retrospektiv gennamgang af journaler. [Incidence of adverse events in hospitals. A retrospective study of medical records, article in Danish, summary in English.] Ugeskr Læger 2001;163:5370–8.

  3. Soop M, Fryksmark U, Köster M, Haglund B. The incidence of adverse events in Swedish hospitals: a retrospective medical record review study. Int J Qual Health Care 2009;21(4):285-291. doi:10.1093/intqhc/mzp025

  4. Wilson RM, Runciman WB, Gibberd RW, Harrison BT, Newby L, Hamilton JD. The Quality in Australian Health Care Study. Med J Aust 1995;163(9):458-71.

  5. Zegers M, Bruijne MC de, Wagner C, Hoonhout LHF, Waaijman R, Smits M, et al. Adverse events and potentially preventable deaths in Dutch hospitals: results of a retrospective patient record review study. Qual Saf Health Care 2009;18(4):297-302. doi:10.1136/qshc.2007.025924