Getting it wrong most of the time? Comparing trialists’ choice of primary outcome with what patients and health professionals want

BACKGROUND: Randomised trials support improved decision-making through the data they collect. One important piece of data is the primary outcome — so called because it is what the investigators decide is the most important. Secondary outcomes provide additional information to support decision-making. We were interested in knowing how important patients and healthcare professionals consider the outcomes (especially the primary outcome) measured in a selection of published trials. METHODS: The work had three stages: (1) We identified a body of late-stage trials in two clinical areas, breast cancer management and nephrology. (2) We identified the primary and secondary outcomes for these trials. (3) We randomly ordered these outcomes and presented them to patients and healthcare professionals (with experience of the clinical area), and we asked them to rank the importance of the outcomes. They were not told which outcomes trial authors considered primary and secondary. RESULTS: In our sample of 44 trials with 46 primary outcomes, 29 patients, one patient representative and 12 healthcare professionals together ranked the primary outcome as the most important outcome 13/46 times or 28%. Breast cancer patients and healthcare professionals considered the primary outcome to be the most important outcome for 8/21 primary outcomes chosen by trialists. For nephrology, the equivalent figure was 5/25. The primary outcome appeared in a respondent’s top 5 ranked outcomes 151/178 (85%) times for breast cancer and 225/259 (87%) times for nephrology even if the primary was not considered the most important outcome. CONCLUSIONS: The primary outcome in a trial is the most important piece of data collected. It is used to determine how many participants are required, and it is the main piece of information used to judge whether the intervention is effective or not. In our study, patients and healthcare professionals agreed with the choice of the primary outcome made by trial teams doing late-stage trials in breast cancer management and nephrology 28% of the time. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13063-022-06348-z.