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Why do two papers on STEP 3 report different headline figures?

Asked 27 Aug 2025Modified 9 months agoViewed 9.9k times
22

I have the full paper rather than the abstract, and the supplementary appendix.

I understand the observation; what I do not understand is the mechanism behind it.

I have read the two review articles that come up first and both assert this without a citation to a primary source.

Can someone derive this rather than assert it?

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HV
askedhelena_vidmar8.5k2727 Aug 2025
Voting to keep this open — it is more specific than it first looks. – mz_4113 9 months ago
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5 Answers

Accepted answer first, then by votes
31

Accepted answer

Because two papers on STEP 3 are usually reporting two different estimands from the same randomisation. The treatment-policy estimand asks what happened to everyone assigned, including those who stopped; the trial-product estimand asks what happens if you keep taking it. The second is always the larger number, and both are legitimate answers to different questions. Then there is the analysis population — randomised, treated, or completers — and the handling of missing data, where a last-observation-carried-forward and a multiple imputation can differ by a point or more. Neither paper is wrong. Read the statistical methods section and you will find both figures defined in it.

Start with what the trial was powered for. Everything else in the publication is secondary, exploratory, or a subgroup, and those three words mean three different things.

Confidence intervals matter more than point estimates when two trials disagree. Two studies reporting fifteen and twenty per cent whose intervals overlap heavily have not disagreed about anything.

Open-label extensions are not the same evidence as the randomised phase. Once everyone knows what they are taking, the reported outcomes acquire a bias that no analysis fully removes.

The cardiovascular outcome programme in this class runs to several large randomised trials — LEADER for liraglutide, SUSTAIN-6 and SELECT for semaglutide, REWIND for dulaglutide — and they are the reason the class is discussed as more than a weight intervention.

The caveat is that trial evidence is about licensed product administered under supervision. None of it transfers automatically to research-grade material of unverified content.

Read the protocol and the statistical analysis plan if the result matters to you. Both are usually published alongside.

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DB
answered · acceptedDr_Ingrid_Baumgartner73k5828 Oct 2025
4Adding a vote because this deserves more of them. – rota_site 3 months ago
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12

Look at the discontinuation rate alongside the efficacy figure. A large effect in the two thirds who stayed is a different result from a large effect in everyone.

Trial populations are selected. Exclusion criteria in this class routinely remove people with significant renal impairment, prior pancreatitis and unstable psychiatric illness, which is exactly the population the results are then quoted for.

Non-inferiority and superiority designs are not interchangeable. A non-inferiority result says the new agent is not meaningfully worse against a pre-specified margin — it does not say it is as good, and it certainly does not say it is better.

Registry entries at ClinicalTrials.gov carry the pre-specified primary endpoint with a timestamp, which is the cheapest available check on whether an endpoint was changed after the data were seen.

Be careful about generalising from a trial population to yourself. The exclusion criteria are usually the most informative page in the supplement.

When two sources disagree, the answer is almost always in the methods section of the one you have not read.

edited 23 Oct 2025 by t_oyelaran — added the method parameters

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TO
answeredt_oyelaran79k4817 Oct 2025
7The number needed to treat is the framing that finally made this concrete for me. – Dr_Sara_Kuusela 7 months ago
8Is the open-label extension included in that figure, or just the randomised phase? – j_wierzbicki 9 months ago
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7

Answer first: read the primary endpoint, the comparator and the population before you read the effect size. Almost every argument on this site about a trial is really an argument about one of those three.

Intention-to-treat and per-protocol analyses answer different questions. ITT asks what happens if you offer the treatment; per-protocol asks what happens if it is taken as directed. The gap between the two is a measure of how tolerable the protocol was.

The relevant detail is that duration decides what can be seen. A 68-week trial can measure weight and glycaemia; it cannot measure anything whose event rate is one per cent per year without enrolling tens of thousands.

If a claim cannot be traced to a named trial with a named endpoint, treat it as a claim rather than as evidence.

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VR
answeredv_ramaswamy68k5714 Sept 2025
5This matches what I was told by a clinician, for whatever that is worth. – sian_llewellyn 3 months ago
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6

The trial answers a narrower question than the headline suggests, and the narrowing is where the useful information is.

Placebo arms in this class are not nothing. Lifestyle-intervention placebo arms in the major obesity trials commonly lose two to three per cent of body weight, so an active-arm figure quoted without its comparator overstates the drug effect by roughly that much.

Meta-analyses in this area are dominated by whichever trial contributed the most participants, so read the forest plot rather than the summary estimate.

I am not a clinician and this is not medical advice; it is a reading of a published protocol.

The short version: check the endpoint, check the comparator, check who was excluded, then look at the number.

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TU
answeredtenth_of_a_unit57k3725 Sept 2025
-3

A trial establishes what happened to a defined group under a defined protocol. Extending it beyond that group is inference, and inference is allowed as long as it is labelled.

A composite endpoint is only as informative as its least serious component. Where a cardiovascular composite combines death, infarction and stroke, ask which component moved, because they are not interchangeable outcomes.

One qualification: absence of a signal in a trial of this size is not evidence of absence for a rare event. It is evidence that the event is rarer than the trial could detect.

Quote the interval alongside the estimate and half the disagreements on this site would not start.

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DK
answeredDr_Tomas_Kral53k386 Oct 2025

Your answer

Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.

Not medical advice. Research-use-only compounds are not approved for human use.