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Why does STEP 1 report two different weight-loss figures?

Asked 18 Apr 2026Modified 7 days agoViewed 4.8k times
2

I have three data points across nine months, which I hope is enough to see a trend.

This is presented as though it settles something, and I am not convinced it does.

I have two documents that appear to disagree, which is what prompted this.

Which parts of this are informative and which are decoration?

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askedpriya_menon13k3518 Apr 2026

4 Answers

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24

Read STEP 1 by arm, because the arm is the unit of randomisation and every figure worth quoting is defined at that level. A programme that randomised several dose levels reports each one separately, with its own sample size and its own interval, and the pooled number that circulates afterwards describes a group nobody was assigned to. Take the primary publication and its supplementary tables rather than a summary of them: one is organised by arm, the other by whichever figure was largest. And check the estimand — what happened to everyone assigned, or what happens to those who kept taking it — because the two answer different questions and are routinely quoted as though they were one.

This is answerable from the published record, but only if you take the placebo arm seriously rather than reading the active arm alone.

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.

Relative to absolute, worked

QuantityValueDerivation
Control-arm event rate8.0 %From the trial table, not the abstract
Hazard ratio0.80Reported
Treated event rate6.4 %8.0 × 0.80
Absolute risk reduction1.6 pp8.0 − 6.4
Number needed to treat631 ÷ 0.016
Relative risk reduction20 %1 − 0.80

The last two rows describe the same finding. Only one of them is used in headlines.

Stated carefully, 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.

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.

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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DO
answeredDr_Malik_Osei19k2711 Jul 2026
8Thank you for separating the surrogate from the outcome. That distinction gets lost constantly. – Dr_Wren_Halliday 10 months ago
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17

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

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.

Specifically, 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.

Where a result is quoted from a conference abstract rather than a peer-reviewed publication, the numbers routinely move between the two. It is worth checking which one you are reading.

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.

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

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answeredh_pergande71k15829 Jun 2026
2Thank you — this is the answer I was looking for. – assay_blank 9 months ago
3The number needed to treat is the framing that finally made this concrete for me. – sian_llewellyn 20 days ago
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13

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.

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.

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

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

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TN
answeredtabular_nums71k4823 Apr 2026
11

To be exact about it, 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.

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.

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

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

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DV
answeredDr_Ilse_Vandenberg113k24823 Jul 2026

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.