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Evidence · Study critique · continued

[2026 update] Confounding by indication, explained with a concrete example posts 91–117

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.

LS
l.sarkissianTL2Member27 Feb 2026#91

Generalisability: do the inclusion/exclusion criteria narrow the population so much that results do not apply to real people asking about it? This is a fair criticism but requires specificity about which real people and why the difference matters.

None of the above is medical advice and I am not qualified to give any.

0 likes 5mo
CN
c.nybergTL227 Feb 2026#92
b.wikstrom, post #26: Multiple comparisons: if a paper reports many outcomes, the chance of a spurious association by random chance is real. Pre-specification of primary outcomes matters and secondary analyses are weaker evidence. Correct me on the arithmetic if it is wrong; I would rather know. Go to post

Understood. Thank you for being specific about the limits of it.

1 like in reply to #26 5mo
P
PWendelboeTL1Member27 Feb 2026#93

Taking post #90 at face value and following it one step further.

Surrogate endpoints are not automatically bad and their validity is compound-specific and population-specific. The question is whether this surrogate has been validated for this use.

Same conclusion as the reply above, reached differently, which is mildly reassuring.

10 likes 5mo
AW
ai.wikstromTL228 Feb 2026#94

A run-in period that excludes non-responders before randomisation changes what the trial is estimating. It is legitimate design and it must be stated in any summary.

If anyone can point at the primary source I would be grateful.

22 likes 5mo
EA
e.almeidaTL2Member28 Feb 2026#95
buffer_margin, post #90: Statistical significance and clinical importance are different and both are needed. A significant difference below the minimal important difference is a real finding of no practical consequence. On reflection I would soften that slightly. Go to post

Building consensus on which criticisms matter: if everyone agrees that the sample size is small but only you think that affects the conclusion, maybe your criticism is more idiosyncratic. That does not make it wrong but it is worth noticing.

The claim is narrower than it sounds, and deliberately so.

0 likes in reply to #90 5mo
NR
n.ramosTL228 Feb 2026#96
Lundqvist, post #17: Attrition is the failure mode most likely to invalidate a result and the least likely to be discussed. Differential attrition between arms is the specific thing to look for. Adding this to the thread rather than to the wiki, because I am not confident enough for the wiki. Go to post

Criticism is more useful when it is narrower. "The trial answers a different question from the one being asked" is actionable; "the trial is flawed" is not.

That holds for the case as described. Change the assumptions and it may not.

3 likes in reply to #17 5mo
I
IHollingworthTL2Member1 Mar 2026 · edited#97

This follows post #94 rather than contradicting it.

Hold a trial to the standard something could actually have met. A criticism that no achievable design could have answered is a criticism of the field rather than of the paper.

15 likes 5mo
TM
t.marchettiTL21 Mar 2026#98

Worth separating two things that post #96 runs together.

The pre-specified endpoint being a weaker proxy than you would like is a real criticism. It is a smaller one than saying the result was chosen after the fact.

Anyone who has looked at this more carefully, please correct the record.

30 likes 5mo
IS
isotonic_sheetTL3Regular1 Mar 2026#99

Post #98 is right about the mechanism and I think understates the practical bit.

Attrition is the failure mode most likely to invalidate a result and the least likely to be discussed. Differential attrition between arms is the specific thing to look for.

1 like 5mo
NK
ni.kravchenkoTL22 Mar 2026#100
IL
integrator_logTL32 Mar 2026#101
SS
s.salgadoTL22 Mar 2026#102
buffer_margin, post #90: Statistical significance and clinical importance are different and both are needed. A significant difference below the minimal important difference is a real finding of no practical consequence. On reflection I would soften that slightly. Go to post

Building consensus on which criticisms matter: if everyone agrees that the sample size is small but only you think that affects the conclusion, maybe your criticism is more idiosyncratic. That does not make it wrong but it is worth noticing.

13 likes in reply to #90 5mo
VT
vial_tableTL2Member2 Mar 2026#103
DOdendaal, post #23: A run-in period that excludes non-responders before randomisation changes what the trial is estimating. It is legitimate design and it must be stated in any summary. The general case is well covered; this is the awkward specific one. Go to post

The arithmetic in post #102 is right; the assumption feeding it is the part to check.

The pre-specified endpoint being a weaker proxy than you would like is a real criticism. It is a smaller one than saying the result was chosen after the fact.

27 likes in reply to #23 5mo
DV
d.vestergaardTL23 Mar 2026#104

Answering the question post #102 raises rather than the one it answers.

Hold a trial to the standard something could actually have met. A criticism that no achievable design could have answered is a criticism of the field rather than of the paper.

I am reporting what happened, not recommending it.

0 likes 5mo
BE
bench_entryTL3Regular3 Mar 2026#105

Generalisability and validity are separate axes. A trial can be internally impeccable and still tell you nothing about the person asking.

That is the version I use. It may not be the version that is correct.

8 likes 5mo
BF
b.friskTL23 Mar 2026#106
j.baptista, post #83: A criticism that would apply equally to every trial in the field is worth stating once and is not a reason to discount a particular paper. Worth one more sentence than it usually gets. Go to post

Statistical significance and clinical importance are different and both are needed. A significant difference below the minimal important difference is a real finding of no practical consequence.

That is my reading. Someone else read the same page differently and was reasonable.

19 likes in reply to #83 5mo
BS
buffer_sheetTL3Regular4 Mar 2026 · edited#107

Multiple comparisons: if a paper reports many outcomes, the chance of a spurious association by random chance is real. Pre-specification of primary outcomes matters and secondary analyses are weaker evidence.

0 likes 5mo
FL
f.lindholmTL24 Mar 2026#108

Post #106 describes the usual case. This is about the unusual one.

Generalisability: do the inclusion/exclusion criteria narrow the population so much that results do not apply to real people asking about it? This is a fair criticism but requires specificity about which real people and why the difference matters.

0 likes 5mo
CC
crossref_checkTL3Wiki editor4 Mar 2026#109

Post #108 is right about the mechanism and I think understates the practical bit.

Surrogate endpoints are not automatically bad and their validity is compound-specific and population-specific. The question is whether this surrogate has been validated for this use.

Scoping that to what I have actually seen rather than what I have read.

0 likes 5mo
JF
j.falkTL25 Mar 2026#110
AW
a.westergaardTL3Regular5 Mar 2026#111

A criticism that would apply equally to every trial in the field is worth stating once and is not a reason to discount a particular paper.

Happy to be corrected if someone holds better data than mine.

1 like 5mo
SO
sa.okonkwoTL25 Mar 2026#112
j.palacios, post #35: Statistical significance and clinical importance are different and both are needed. A significant difference below the minimal important difference is a real finding of no practical consequence. Go to post

Criticism is more useful when it is narrower. "The trial answers a different question from the one being asked" is actionable; "the trial is flawed" is not.

Happy to expand any of that if it is the useful part.

0 likes in reply to #35 5mo
JD
j.delacroixTL3Regular5 Mar 2026#113

Attrition is the failure mode most likely to invalidate a result and the least likely to be discussed. Differential attrition between arms is the specific thing to look for.

That much is documented. The rest is how I have interpreted it.

25 likes 5mo
RM
ra.mensaTL26 Mar 2026#114

Picking up post #113: that is the part I would want checked first.

A run-in period that excludes non-responders before randomisation changes what the trial is estimating. It is legitimate design and it must be stated in any summary.

I am not the right person to answer the follow-up to this.

12 likes 5mo
M
MSaarinenTL3Regular6 Mar 2026#115

Sensible. I would want the same detail before I acted on it either.

4 likes 5mo
BB
b.brandtTL26 Mar 2026#116
a.jansen, post #49: Generalisability: do the inclusion/exclusion criteria narrow the population so much that results do not apply to real people asking about it? This is a fair criticism but requires specificity about which real people and why the difference matters. Where I would look next, rather than where I would stop. Go to post

Generalisability: do the inclusion/exclusion criteria narrow the population so much that results do not apply to real people asking about it? This is a fair criticism but requires specificity about which real people and why the difference matters.

Nothing above should be read as advice about what anyone else should do.

0 likes in reply to #49 5mo
DM
d.magalhesTL2Member7 Mar 2026 · edited#117
KForsberg, post #11: Taking post #10 at face value and following it one step further. Building consensus on which criticisms matter: if everyone agrees that the sample size is small but only you think that affects the conclusion, maybe your criticism is more idiosyncratic. That does not make it wrong but it is worth noticing. Old habit: I write down the… Go to post

Post #113 describes the usual case. This is about the unusual one.

A criticism that would apply equally to every trial in the field is worth stating once and is not a reason to discount a particular paper.

0 likes in reply to #11 5mo

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