Powering new studies based on old event rates...

[irene stratton]

Some time ago I was sent a paper to review which was about powering
studies for an outcome in diabetes. Due to landmark trials in Type 1
and Type 2 diabetes published in 1990s control of hypertension and
hyperglycaemia is now better than it was. Hence trials powered on
event rates in previous studies end up being underpowered because
event rates are now lower. I can't find this paper and wonder if
anyone else knows of something like this.

[ציפי שוחט‎]

Dear Irene.

I've seen this same phenomena in MS and Myoblastic Glioma, where after a blockbuster medication the Placebo group event rates fall.

I've also been told by a MD that if there is a known, reasonably effective, treatment, he won't propose participating in a clinical study to his sicker patients.

Hope this helps.

Tzippy

2012/5/24 irene stratton <irene.s...@nhs.net>

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[Munya Dimairo]

does this mean that we need to adopt adaptive approach in our designs? There are many situations where the assumed assumptions turns out not to be true irrespective of the lapse in time or close to the truth. It's not only in the diabetes area but it cuts across medical research.


Cheers

Munya

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Date: Thu, 24 May 2012 16:30:21 +0300

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Subject: Re: {MEDSTATS} Powering new studies based on old event rates...

[Steve Simon, P.Mean Consulting]

It's not the same thing, but a while back an article appeared which
claimed that Epidemiology had discovered all the big effects in public
health and that the only things left to discover were being swamped by
the biases inherent in epi studies.

G Taubes. Epidemiology faces its limits Science. 1995;269(5221):164
-169.
http://geography.ssc.uwo.ca/faculty/baxter/readings/Taubes_limits_epidemiology_Science_1995.pdf


Perhaps this is true in many fields. The big effects, which are easy to
discover, have been spoken for and everything left is much more subtle,
requiring larger sample sizes.

It's also a truism that early in the history of a disease when there is
no available alternative therapy and you have to compare versus a
placebo, you get by with smaller sample sizes compared to later in the
history of the disease and you are comparing against an active control.

That doesn't directly answer your question, but I hope it helps.

Steve Simon, n...@pmean.com, Standard Disclaimer.
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