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Background: A core outcome set (COS) has been developed through international consensus to reduce selective reporting and research waste, and guide outcome choice in alcohol brief intervention (ABI) research.Objectives: This study aimed to estimate order effects among questions in the ORBITAL COS.Methods: Adults, aged over 18 years who searched online for alcohol-related help were invited to complete a survey containing the COS items. The order of four item clusters was randomised following a factorial design with 24 conditions (double blind). Primary outcomes were order effects among the COS items and patterns of abandonment of the questionnaire.Results: Between 21st October and 26th November 2020, we randomised 7334 participants, of which 5256 had responded to at least one question and were available for primary complete-case analyses and imputed sensitivity analyses. Current non-drinkers were excluded. Median completion time for the COS was 4 minutes 16 seconds. We found evidence of order effects among COS clusters, including higher self-reported average consumption and odds of harmful and hazardous drinking among those who first answered questions on recent consumption and impact of alcohol use. Lower self-reported recent consumption was found among those first asked about average consumption. Quality of life was reported as lower among those who first responded to questions on impact of alcohol use, which in turn was lower among those who first answered question on average consumption and quality of life. Attrition was lowest when average consumption was asked first, and highest when quality of life or impact of alcohol use asked first.Conclusions: Researchers designing studies should note that question order effects may exist. At a minimum, all study participants should be asked the same questions in the same order. There is no perfect question order; rather, researchers should be guided by the nature of the studied population, recruitment, additional questions, concerns about under-reporting, screening for inclusion, and retention concerns.Trial registration: The trial was prospectively registered (ISRCTN Registry ISRCTN17954645) and received ethical approval on 2020-07-01 from the Swedish Ethical Review Authority (Dnr 2020-01799).Registered report: International Registered Report Identifier (IRRID): PRR1-10.2196/24175

BackgroundA core outcome set (COS) for trials and evaluations of the effectiveness and efficacy of alcohol brief interventions (ABIs) has recently been established through international consensus to address the variability of outcomes evaluated. ObjectiveThis is a protocol for studies to assess if there are order effects among the questions included in the COS. MethodsThe 10 items of the COS are organized into 4 clusters. A factorial design will be used with 24 arms, where each arm represents 1 order of the 4 clusters. Individuals searching online for help will be asked to complete a questionnaire, and consenting participants will be randomized to 1 of the 24 arms (double-blind with equal allocation). Participants will be included if they are 18 years or older. The primary analyses will (1) estimate how the order of the clusters of outcomes affects how participants respond and (2) investigate patterns of abandonment of the questionnaire. ResultsData collection is expected to commence in November 2020. A Bayesian group sequential design will be used with interim analyses planned for every 50 participants completing the questionnaire. Data collection will end no more than 24 months after commencement, and the results are expected to be published no later than December 2023. ConclusionsHomogenizing the outcomes evaluated in studies of ABIs is important to support synthesis, and the COS is an important step toward this goal. Determining whether there may be issues with the COS question order may improve confidence in using it and speed up its dissemination in the research community. We encourage others to adopt the protocol as a study within their trial as they adopt the ORBITAL (Outcome Reporting in Brief Intervention Trials: Alcohol) COS to build a worldwide repository and provide materials to support such analysis. Trial RegistrationISRCTN Registry ISRCTN17954645; http://www.isrctn.com/ISRCTN17954645 International Registered Report Identifier (IRRID)PRR1-10.2196/24175