Core Outcome Measures in Effectiveness Trials

A Core Outcome Set for the Benefits and Adverse Events of Bariatric and Metabolic Surgery: The BARIACT Project

General Information


Bariatric and metabolic surgery is used as a treatment for patients with severe and complex obesity. However, there is a need to improve outcome selection and reporting in bariatric surgery trials. A Core Outcome Set (COS), an agreed minimum set of outcomes reported in all studies of a specific condition, may achieve this. Here, we present the development of a COS for BARIAtric and metabolic surgery Clinical Trials—the BARIACT Study.

Methods and Findings

Outcomes identified from systematic reviews and patient interviews informed a questionnaire survey. Patients and health professionals were surveyed three times and asked to rate the importance of each item on a 1–9 scale. Delphi methods provided anonymised feedback to participants. Items not meeting predefined criteria were discarded between rounds. Remaining items were discussed at consensus meetings, held separately with patients and professionals, where the COS was agreed. Data sources identified 2,990 outcomes, which were used to develop a 130-item questionnaire. Round 1 response rates were moderate but subsequently improved to above 75% for other rounds. After rounds 2 and 3, 81 and 14 items were discarded, respectively, leaving 35 items for discussion at consensus meetings. The final COS included nine items: “weight,” “diabetes status,” “cardiovascular risk,” “overall quality of life (QOL),” “mortality,” “technical complications of the specific operation,” “any re-operation/re-intervention,” “dysphagia/regurgitation,” and “micronutrient status.” The main limitation of this study was that it was based in the United Kingdom only.


The COS is recommended to be used as a minimum in all trials of bariatric and metabolic surgery. Adoption of the COS will improve data synthesis and the value of research data. Future work will establish methods for the measurement of the outcomes in the COS.

The development of a COS for BARIAtric and metabolic surgery Clinical Trials

Karen D. Coulman ,
James Hopkins,
Sara T. Brookes,
Katy Chalmers,
Barry Main,
Amanda Owen-Smith,
Robert C. Andrews,
James Byrne,
Jenny L. Donovan,
Graziella Mazza,
Barnaby C. Reeves,
Chris A. Rogers,
Janice L. Thompson,
Richard Welbourn,
Sarah Wordsworth,
Jane M. Blazeby,
BARIACT working group


PLOS Medicine
Further Study Information

Funding source(s):

Health Area

Disease Category
Endocrine & metabolic

Disease Name

Target Population

Age Range
18 - 110


Nature / type of Intervention


Consensus meeting
Delphi process
Systematic review

Stakeholders Involved

Clinical experts
Consumers (patients)

Study Type

COS for clinical trials or clinical research
COS for practice
Patient perspectives
Systematic review of outcomes measured in trials
Systematic review of qualitative research

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