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EVIDENCE-BASED-HEALTH  January 2011

EVIDENCE-BASED-HEALTH January 2011

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Subject:

Re: Can RCT help establish causation?

From:

Marcelo <[log in to unmask]>

Reply-To:

Marcelo <[log in to unmask]>

Date:

Mon, 31 Jan 2011 10:42:50 -0200

Content-Type:

text/plain

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Parts/Attachments

text/plain (127 lines)

Dear all ...what an amazing discussion...in theory the randomization process leads to balanced groups... Considering the known and unknown confounders...so the great determinant of causation is the external validity of the study...

Enviado via iPhone

Em 30/01/2011, às 23:08, Richard Saitz <[log in to unmask]> escreveu:

> Hi Ben, Paul, Colleagues,
> I can confirm that EBM (the journal) is interested in such Perspectives and
> also in publishing expanded more detailed versions of what appears in ISEHC.
> We have sought such submissions and they are now coming in, and I believe
> will help to disseminate such information widely.
> Best
> Rich
>
> Richard Saitz MD, MPH, FACP, FASAM
> Editor, Evidence-based Medicine (EBM)
>
> http://ebm.bmj.com/
>
> -----Original Message-----
> From: Evidence based health (EBH)
> [mailto:[log in to unmask]] On Behalf Of Paul Glasziou
> Sent: Sunday, January 30, 2011 6:52 PM
> To: [log in to unmask]
> Subject: Re: Can RCT help establish causation?
>
> Good idea Tom,
> Ben - one simple option is the ISEHC Newsletter, from which some articles
> are also picked up for the EBM Journal (and I'm pretty sure this would be).
> Even an annotated reference list would be useful. To add my two cents:
> Randomisation comes closer to eliminating confounding than other methods,
> and so can be trusted to correctly identify smaller effects.
> But for very big effects (smoking and lung cancer) observatioinal studies
> can be sufficient (but see Bradford-Hill guidelines).
> The crucial issue is whether the effect size is greater than the plausible
> biases
> (see Glasziou et al . When are randomised trials unnecessary? Picking signal
> from noise. BMJ. 2007 Feb 17;334(7589):349-51. and
> Howick J et a The evolution of evidence hierarchies: what can Bradford
> Hill's 'guidelines for causation' contribute? J R Soc Med. 2009
> May;102(5):186-94)
> Cheers
> Paul Glasziou
> ________________________________________
> From: Evidence based health (EBH) [[log in to unmask]] On
> Behalf Of Tom Jefferson [[log in to unmask]]
> Sent: 30 January 2011 17:23
> To: [log in to unmask]
> Subject: Re: Can RCT help establish causation?
>
> Ben and all. I think it is important that your summing up and the many
> excellent contributions to this debate get written up. As you pointed out,
> there is a movement underway to try to subvert the value of the RCT. The
> RCT, if properly designed and conducted, represents the only near-perfect
> tool to test causation at our disposal as it eliminates the play of
> alternative explanations of the results observed. It is as near as we are
> going to get (at least in our lifetime) to a Galilean experiment.
>
> The validity of the inferences from its results are still limited by the
> problem of induction (Hume's problem), but Fisher's probabilistic "patch"
> makes their limits at least explicit and quantifiable.
>
> Thank you for a delightful debate.
>
> Tom.
>
> On 30 January 2011 17:29, Djulbegovic, Benjamin
> <[log in to unmask]<mailto:[log in to unmask]>> wrote:
> Dear all
> First, I want to thank many of you who responded either directly to me or to
> the entire group with the phenomenal line of thoughtful insights related to
> the question if RCT can establish causation. Once again, participation in
> this group has proved so rewarding - there is no question, big or small,
> theoretical or practical that goes unanswered at rather deep level.
>
> The immediate reason for my question was motivated by increasing number of
> writings in the philosophical literature that question feasibility of
> developing hierarchy of evidence- one of the most important contribution of
> EBM, I should add. While there are several lines of this critique, the most
> fundamental- and thus most important- is the claim that, in principle, the
> inferences drawn from RCTs are not epistemologically superior to
> observational studies. In particular, the criticism was leveled against RCT
> as the purported mechanism to establish causation (as randomization allows
> equal distribution of all known and UKNOWN confounders apart from the
> intervention of interest). The critics (in particular Worrall) has asserted
> that ."given that there are indefinitely many possible confounding
> factors...the probability that the groups are unbalanced ...is high" and
> hence inferences from RCTs are not epistemologically different from those
> drawn from the observational research.
>
> Some of you graciously sent me several papers refuting some of Worral's
> critique (I am still reading some of the material you sent- so, some what I
> am writing here may still change), but most poignant repudiation of Worral's
> criticism came from Stephen Senn. His paper (Senn, SJ. Baseline Balance and
> Valid Statistical Analyses: Common Misunderstandings, Applied Clinical
> Trials 2005; 14: 24-27) should be required reading for all EBMers (although
> after reading one will probably say, this is so obvious!, it certainly was
> an eye opener for me, not exactly someone who is in this business since
> yesterday!). As Stephen pointed out (proved), "there is no point worrying
> about the distribution of unmeasured covariates" as we can still draw the
> valid inferences based on information we have (what we do NOT know CANNOT be
> factored in the way we draw our conclusions or make our inferences). The
> same argument cannot apply to observational studies as we don't have formal
> machinery (randomization) to draw the accurate inferences about the
> probability statements.
> Finally, several folks cogently argued that randomization is indeed the
> necessary (although not sufficient reason, as it may be subverted etc) to
> establish causation.
> This all indicate that indeed experimental, RCT design remains
> epistemologically superior to observational studies (no big news for the
> members of this group, but fundamentally really big news).
> Thanks again to all of you for the phenomenal discussion and contribution
> Ben djulbegovic
>
>
>
> --
> Dr Tom Jefferson
> Scientific Editor PLoS ONE
> Reviewer, Cochrane Acute Respiratory Infections Group
> tel 0039 3292025051
>
> ______________________________________________________________________
> This email has been scanned by the MessageLabs Email Security System.
> For more information please visit http://www.messagelabs.com/email
> ______________________________________________________________________

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