Box 2. Definitions of harm used. Adapted from Cooper et al. ²⁹ Example incidents for each harm severity can be found in Supplementary Box S1.²⁹ .

Harm severity	Definition of harm severity
No harm/near miss	Incidents that occurred but caused no harm to the patient. This includes incidents that were mitigated before they caused harm
Mild harm	Incident in which: (a) patient was harmed, with mild and short-term impact, on physical, mental, or social functioning, that was expected to resolve in a few hours; (b) patient was harmed but required no or minimal intervention/treatment, for example, antiemetic, oral antibiotic, or repeat of a minor procedure such as vaccination or insertion of contraceptive implant; and/or (c) patient or their loved ones experienced transient emotional distress but no long-term consequences and incident report contains words, for example, angry, anxious, confused, distressed, frightened, frustrated, humiliated or upset, that might describe a feeling that occurs at the time of the incident but soon passes
Moderate harm	Incident in which: (a) patient was harmed, causing a medium-term impact on physical, mental, or social functioning that was expected to resolve in days; (b) patient required medical intervention in the form of treatment, for example, antibiotics or intravenous fluids; (c) patient required short-term hospitalisation for assessment and/or minor treatment in either an emergency department or a hospital ward; and/or (d) patient or their loved ones experienced psychological difficulty of a more long-standing nature but not requiring formal treatment, for example, as indicated by evidence in the report of more long-standing anxiety, insomnia, or low mood
Severe harm	Incident in which: (a) patient was harmed, causing a major long-term or permanent impact on physical, mental, or social function or shortening of life-expectancy; (b) patient was harmed and required major medical or surgical intervention that, most often, was delivered in a hospital setting, for example, cardioversion, any major surgery; (c) patient was harmed and required prolonged hospitalisation or admission to a high dependency unit and/or intensive care unit; and/or (d) patient or their loved ones experienced enduring psychological difficulty that required specialist treatment, for example, as indicated in the report by evidence of chronic anxiety or depression or psychosis
Death	Incident in which, on the balance of probabilities, death of the patient was caused or brought forward in the short term by the incident
Insufficient details	Insufficient information about the incident to evaluate the severity of harm