Core Outcome Measures in Effectiveness Trials

Adverse event outcomes

  • Any specifically named adverse events (AEs) (for example, fatigue or pain) should be categorised under the appropriate taxonomy domain, rather than within the Adverse event domain, with the second component identifying the outcome as a harm (rather than benefit) outcome.
  • For example, the COS for colorectal cancer surgery (McNair 2016) includes faecal urgency, which is a potential adverse effect of the surgery. This would be classified as a physiological outcome, under the Gastrointestinal domain, but the second component would identify it as an adverse outcome.
  • Note that death is not necessarily classified as an AE. For example, if the purpose of surgery is to improve length of survival, then "death" would be a benefit outcome. However, death related to intervention (e.g. "treatment-related death") would be a harm outcome and should therefore be classified under Mortality/survival with a secondary component identifying it as an adverse outcome.
  • In contrast, the AE domain only includes outcomes explicitly labelled as some form of unintended consequence of the intervention, such as "adverse events", "adverse effects", "adverse reactions", "complications", "toxicity"" or "sequelae".
  • If specific AEs are listed as examples of a general AE outcome, such as "Adverse events (e.g. pain, fatigue, hospitalisation)", then each specifically named AE should be classified within the appropriate domain (with the second component identifying it as a harm outcome) but the general term ("Adverse events") should also be classified within the AE domain.
  • This AE domain is also relevant for broad-level complications related to the intervention (e.g. "Anaesthetic Complications" or "Operative morbidity"). However broad-level complications linked to a condition (e.g. "Bowel-related complications") should be classified within the relevant physiological domain (e.g. Gastrointestinal), with the second component identifying it as a harm outcome.
  • The AE domain, which is not intended to include any specifically named adverse events, is important as it indicates whether or not trialists or researchers considered the need to record events that may not necessarily be prespecified ahead of time.


McNair, A.G.K., Whistance, R.N., Forsythe, R.O., Macefield, R., Rees, J., Pullyblank, A.M. et al. (2016) Core outcomes for colorectal cancer surgery: a consensus study. PLoS Med, 13: e100207

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