SURMOUNT-3 extension data: what happens after the trial stops

SURMOUNT-3 met its primary endpoint and did not meet one of its hierarchically tested secondary endpoints, a result which appears in the paper and in almost none of the reporting. Under a pre-specified testing hierarchy a failure at that point formally precludes claims on the endpoints below it, whatever the nominal p-values show.

The endpoint hierarchy was pre-specified in the statistical analysis plan and is reproduced in the supplementary appendix. Readers relying on the abstract will not see it. The Journal reads the analysis plan before the paper for exactly this reason.

Cross-trial comparison is the commonest error in coverage of this field. Populations differ in baseline weight, diabetes status and lifestyle-intervention intensity; durations differ; estimands differ. Two programmes reporting 15% and 20% may or may not reflect a difference between the drugs, and only a head-to-head trial settles it.

"The mean is not the interesting part and it never has been," said Dr Ingrid Haldorsen, clinical epidemiologist. "Show me the decile plot. That is where the clinical question lives."

The full publication is in the Journal’s trial-data explorer with the estimand, the comparator, the duration and the withdrawal rate recorded alongside the headline figure.