Re: st: Re: sample size calculation

[Richard Williams <Richard.A.Williams.5@nd.edu>]

At 12:28 PM 9/30/2004 +0900, Joseph Coveney wrote:
> It seems as Ricardo's authors are assaying nicotine or its metabolites in 
> some
> tissue (placenta, perhaps).  In pharmacokinetics, variation often *is*
> expressed in terms of the coefficient of variation, as Clint suggests.  If
> Ricardo's authors intended to say that the standard deviation is 15% 
> instead of
> 15 ng/mg, and if they contemplated using Bonferroni's inequality to adjust
> alpha for two comparisons among the three groups, then
>
> -sampsi 100 115, alpha(0.025) power(0.8) sd1(15) sd2(15)-
>
> gives 43.  Here, I'm assuming that power, not beta, is 80%.  It's possible 
> that
> Ricardo's authors' article is peppered with unintentional errors and 
> omissions
> in describing things, such as power and the scale for variation.
I think you meant

sampsi 100 110, alpha(0.025) power(0.8) sd1(15) sd2(15)

At least, that is what gives me an N of 43; the original command gives Ns 
of 20.

Yes, part of what confuses me about the original problem is the use of both 
percents and non-percents.  You get the feeling something is missing or 
misstated; but then I am far more used to doing secondary analysis of large 
data sets than I am problems like this.  I suppose another possibility is 
that the 15 ng/mg is correct but then it gets converted into some sort of 
percentage?


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Richard Williams, Notre Dame Dept of Sociology
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