Outcome Classification

Use of outcome taxonomies

Taxonomy: explanation and examples

We have developed a new taxonomy suitable for classification of outcomes included in all trials, COS, systematic reviews and trial registries (see table 1 in https://doi.org/10.1016/j.jclinepi.2017.12.020).

  • This taxonomy is intended for the classification of what, rather than how, outcomes are measured.
  • The taxonomy relates to outcomes measured at an individual-patient level (including those relating to the direct impact of the individual patient’s treatment or condition on wider society, for example resource use or carer burden) but is not intended to cover outcomes relating to the health or functioning of wider society (for example, family or community health). Therefore, health promotion or public health outcomes from trials of family- or community-based interventions can be classified using our taxonomy if they relate to an individual’s condition or care, but not if they are measured at the family or community level.
  • Classifications of outcomes using this taxonomy are intended to comprise two components, the first defining the outcome structure (as defined in the 38-item scale described in the table below) and the second specifying whether the outcome is being measured as a benefit or a harm outcome.
  • Outcomes which cover multiple domains (for example, composite outcomes) should be classified in all relevant domains.
  • We are confident that our taxonomy provides a sufficiently comprehensive basis for the categorisation of outcomes included in clinical trials in general, and hope that this taxonomy will assist COS developers who need to categorise outcomes, for example as part of their Delphi survey. However, we would welcome feedback from researchers applying the taxonomy in their clinical settings in order to demonstrate further validation of the taxonomy or to highlight any necessary changes.
  • Explanations and examples of outcomes within each outcome domain are given in the table below. We will monitor use of the taxonomy and collate feedback and common queries, and the explanation table will be regularly updated to address ambiguities and answer frequently asked questions.
  • Note that outcome descriptions in trials, COS and SRs are not always sufficiently detailed to facilitate confident classification. Researchers are encouraged to give as much detail as possible when defining outcomes in order to aid classification.
  • This taxonomy is consistent with the ‘areas’ proposed by OMERACT (1) but provides further granularity, helpful for the development of core outcome sets. The authors do not suggest that trials, COS or SRs should necessarily include outcomes from each of the core areas however.

(1) Boers M, Kirwan JR, Wells G, Beaton D, Gossec L, d’Agostino MA, et al. Developing core outcome measurement sets for clinical trials: OMERACT filter 2.0. J Clin Epidemiol 2014;67:745e53.

Dodd SR, Clarke M, Becker L, Mavergames C, Fish R, Williamson PR. (2018) A taxonomy has been developed for outcomes in medical research to help improve knowledge discovery. Journal of Clinical Epidemiology, 96:84-92