[R] Repeated tests against baseline

[Cody Hamilton]

Thank you Greg - I will read these carefully.  Lancet should carry great weight with the clinical audience.

Do you know of any references that address the fact that the paired differences at 30 days, 60 days, etc. are typically correlated?

Regards,
   -Cody

-----Original Message-----
From: Greg Snow [mailto:Greg.Snow at intermountainmail.org]
Sent: Wednesday, September 26, 2007 3:24 PM
To: Cody Hamilton; r-help at stat.math.ethz.ch
Subject: RE: [R] Repeated tests against baseline

Here are a couple to look at, they may be helpful and the references in
them may give you a specific example that you can use (read them through
yourself, then decide if you want your docs to read them).

Kenneth F Schulz and David A Grimes (2005), "Multiplicity in randomised
trials I: endpoints and treatments", The Lancet, 365: 1591-95

Kenneth F Schulz and David A Grimes (2005), "Multiplicity in randomised
trials II: subgroup and interim analyses", The Lancet, 365: 1657-61


Hope this helps,


--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at intermountainmail.org
(801) 408-8111



> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of Cody Hamilton
> Sent: Wednesday, September 26, 2007 3:15 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Repeated tests against baseline
>
> I came across a post by Karl Knoblick regarding the modeling
> of longitudinal data (see
> https://stat.ethz.ch/pipermail/r-help/2007-May/132137.html).
> I am often asked by physicians to perform what Karl refers to
> in his post as option 1: to perform paired t-tests against
> baseline at each follow up time point (30 days, 90 days, 6
> months, etc.).  Unlike Karl's example, however, many of the
> trials I am involved in are one-armed (so there are no
> across-trial-arms comparisons).
>
> No matter how hard I try to explain to physicians why this
> approach is not the best, it has typically been to no avail.
> I am wondering if anyone knows of a paper I can quote
> instead?  One (or more) from the cardiovascular literature
> would be especially precious to me.
>
> Best regards,
>    -Cody Hamilton
>
>
>
>       [[alternative HTML version deleted]]
>
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