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From |
Richard Williams <Richard.A.Williams.5@nd.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Re: sample size calculation |

Date |
Wed, 29 Sep 2004 22:52:25 -0500 |

At 12:28 PM 9/30/2004 +0900, Joseph Coveney wrote:

It seems as Ricardo's authors are assaying nicotine or its metabolites in someI think you meant

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.

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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**References**:**st: Re: sample size calculation***From:*Joseph Coveney <jcoveney@bigplanet.com>

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