Matt
Could you be thinking of Assmann et al. Subgroup analysis and other
(mis)uses of baseline data in clinical trials. Lancet 2000; 355: 1064-69
Best explanation of the issues relating to subgroup analyses that I have
come across.
Best wishes
Janet
Janet Robertson
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-----Original Message-----
From: Evidence based health (EBH)
[mailto:[log in to unmask]] On Behalf Of Matt Williams
Sent: 09 May 2007 12:24
To: [log in to unmask]
Subject: Re: Subgroup analyses - are they ever best evidence
There was a review in The Lancet ~ 6-7 years ago that mentioned this
(afraid I can't be any more precise than this). Their conclusion was
that subgroup analyses are rarely valid, especially if they lie in the
opposite direction to the whole-group results (which is when they are
interesting....)
HTH,
Matt
Brian Alper MD wrote:
> I would suggest a pre-planned stratified randomization with analyses
> within the stratified groups could provide level 1 evidence. This
> could be called a "subgroup analysis" but would be the equivalent of
> independent randomized trials being reported as a single trial.
>
> All of the usual considerations for bias would have to be considered
> at the level of the "subgroup" -- adequate sample size, adequate
> follow-up rates, intention-to-treat analysis, etc.
>
> In addition consider whether the effects of other trial activity
> (including statistical evaluations) could in any way bias the chances
> of finding and reporting significant differences in the "subgroup".
>
>
> If the randomization was not stratified by the subgrouping, then the
> clustering of confounding factors along with the "subgroup factor"
> could nullify the initial reason for randomization. Adjusting for
> recognized confounding factors cannot exclude bias from unrecognized
> confounding factors.
>
> --------------------------------------
> Brian S. Alper, MD, MSPH
> Editor-in-Chief, DynaMed (www.DynamicMedical.com) Medical Director,
> EBSCO Publishing 10 Estes St.
> Ipswich, MA 01938
> office (978) 356-6500 extension 749
> cell (978) 804-8719
> fax (978) 356-6565
> home (978) 356-3266
> "It only takes a pebble to start an avalanche."
> -----Original Message-----
> From: Evidence based health (EBH)
> [mailto:[log in to unmask]] On Behalf Of Olive
> Goddard
> Sent: Wednesday, May 09, 2007 4:14 AM
> To: [log in to unmask]
> Subject: Re: Subgroup analyses - are they ever best evidence
>
> Dear Colleagues,
>
> Would anyone be prepared to respond to this query from Gayle Robins.
>
> All good wishes,
>
> Olive
>
>
>
>>>> "Robins, Gayle" <[log in to unmask]> 09/05/2007 06:01
>>>>
> Hello Mrs Goddard
>
> When I evaluate a clinical trial, I use the Oxford Centre for Evidence
> Based Medicine's recommendation as a guideline for whether the
> information provided by the trial could be considered as best
> evidence.
> I note that individual randomised controlled trials with narrow
> confidence intervals are considered as level 1b on your levels of
> evidence chart. Please can you advise me where, if at all, subgroup
> analyses of these level 1b randomised clinical trials would fall on
> the best-evidence hierarchy.
>
> I realise that there are many different types of subgroup analysis:
> those that are defined apriori versus retrospectively or on an ad-hoc
> basis; those that address the same outcome of interest that the
> randomised controlled trial was designed to assess versus other
> outcomes; and those that are part of a plethora of subgroup analyses
> of the same trial and so require correction for multiplicity, to name
> a few.
>
> Are any subgroup analyses of level 1b randomised controlled trials
> ever considered best evidence?
>
> Thanks you for your time taken to read this email. I would appreciate
> any advice that you can give me, or people that I could contact, in
> this regard.
>
> Gayle Robins
> Team Leader
> Clinical Trials Insight
>
> Adis International
> Wolters Kluwer Health
> Ph: 09 4770700
> Email: [log in to unmask]
--
http://acl.icnet.uk/~mw
http://adhominem.blogsome.com/
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