Re: st: Sample size calculation

[Ron�n Conroy <rconroy@rcsi.ie>]

On 26 DF�mh 2005, at 14:19, <slaowattana@pol.net>  
<slaowattana@pol.net> wrote:


> We are planning to measure some cytokines in patients with MS  
> comparing
> between a group with treatment and control, but there have not been
> literatures regarding these measurements, so we do not have an  
> estimated
> mean and standard deviation. Is there a way to estimate a sample size?
> (our IRB really wants to see sample size estimate.) Thanks.
You really are in the dark, then.

There are several approaches. The Resource Equation method

http://embryo.ib.amwaw.edu.pl/invittox/er/ER/ER%2029.pdf see page 9

is useful in a preliminary experiment. It's based on the idea that  
the amount of information in each new piece of data diminishes as the  
sample size increases.

It allows you to estimate the sample size needed to ascertain whether  
a study would be useful or not. It is often used in animal research  
where investigators have no idea at all of what they might find.

Ron�n Conroy
rconroy@rcsi.ie




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