SELECT: what the trials say vs what this community says
The title is the argument: SELECT: what the trials say vs what this community says. Here is the rest of it.
Intention-to-treat analyses everybody randomised regardless of what they did afterwards. Completer analyses only those who finished. The second is systematically more flattering and both are legitimate if labelled.
On means, which this board treats as targets and which are nothing of the sort.
A reported mean body weight change is the centre of a distribution that in these trials is very wide. Substantial numbers of participants did much better, and substantial numbers did considerably worse while remaining on the drug and in the analysis.
Quoting the mean as an expectation therefore misleads in both directions: it makes ordinary results look like failures and it makes exceptional results look normal. If a paper publishes the distribution — and several do, in the appendix — look at that instead. It is far more informative than the number in the abstract.
Why comparing across trials almost never works, with the specific failure modes.
Different populations: an obesity programme and a diabetes programme enrol different people with different baseline characteristics. Different endpoints: body weight change, glycaemic control and cardiovascular events are not convertible. Different durations: 68 weeks and 72 weeks are not the same, and the curves have not flattened by either.
Different analysis populations: one paper reports intention-to-treat, another emphasises completers. Different support: some trial designs include structured lifestyle contact that no member of this board receives.
Stack those and the "X beats Y" tables that circulate here are comparing five things at once and attributing the difference to the molecule.
Screenshot none of this. Read the whole thread, including the parts where I am told I am wrong.
best — the order this archive was captured in
Cardiovascular outcome trials are powered for events, not for weight, and are typically run in a different population with different inclusion criteria. Reading a weight number out of one is reading a secondary endpoint.
Added the trial identifier to the title so this thread is findable in two years.
Push back: an open-label extension tells you about the people who stayed. That is a different question.
Yes — the interval is the finding. A point estimate with a wide interval is a hypothesis in a nice font.
Same. A press release is a claim about a result; the publication is the result.
That is the 68-week readout, not the 72-week one. Different trial, different duration.
Discontinuation rates are a tolerability result. A trial with a strong efficacy number and heavy discontinuation is telling you two things and people only quote one.
What did the confidence interval look like?
SURPASS is the diabetes programme and reports glycaemic endpoints
Compared myself to a trial mean for about six months before realising the trial arm had dietitian contact every fortnight.
trial populations get support that nobody on this board gets
Read a press release and the publication three months apart. The hedging in the second one was substantial.
Do you have the publication or the press release?
Do you have the publication or the press release?
Adding the check nobody runs — the registered protocol is public and takes two minutes to compare.
A confidence interval is the range of effects compatible with the data. Two trials with overlapping intervals have not disagreed, whatever their point estimates look like next to each other.
How to read one of these papers in fifteen minutes, in the order that actually helps.
Start with the registered protocol and check the primary endpoint against what is reported. Then the methods: who was included, what the comparator was, how long the randomised phase ran. Then the discontinuation numbers, which are a tolerability result and are usually in a supplementary table.
Only then the efficacy figure, and read the interval rather than the point estimate. Finish with the limitations section, which is where the authors say what they actually think.
Fifteen minutes, and you will know more than any thread summarising it.
Spent an evening with the appendix tables and found the subgroup detail that the entire thread had been speculating about.
Went looking for the registered protocol to see whether the endpoint had changed. It had not, which was reassuring and worth checking.
That is a relative risk reduction. Quoting it without the absolute numbers overstates the case considerably.
Relative risk reduction without the baseline rate is uninterpretable. A large relative reduction on a small absolute risk is a small absolute benefit.
The press release said that; the publication says something more hedged. Worth reading both.
intention to treat versus completers changes the number substantially
Is that intention-to-treat or completers?
the confidence interval is the finding, the point estimate is the headline
- 1A confidence interval is the range of effects compatible with the data. Two…12 comments in this branch · started by u/hedda_adeyemi
- 2Same. A press release is a claim about a result; the publication is the…6 comments in this branch · started by u/blunt_coldbox_notes