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Date:   Mon, 8 May 2006 14:52:28 -0400
Reply-To:   Kevin Roland Viel <kviel@EMORY.EDU>
Sender:   "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:   Kevin Roland Viel <kviel@EMORY.EDU>
Subject:   Re: help on power calculation
In-Reply-To:   <5ac3d2950605081141j44c2dae0q3ff5ea40bfae76fc@mail.gmail.com>
Content-Type:   TEXT/PLAIN; charset=US-ASCII

On Mon, 8 May 2006, wraong wrote:

> All I knew were: > It's a case-control study on one certain exposure and a certain cancer. I > don't know what the exposure is, I just know that it is a continous variable > and will be categorized according to quartiles, compare the upper quartile > with the lower one, the null hypothesis is OR=1.

First of all, you may be throwing away data. Why would you categorized? What were the reasons provided to you?

Second of all, you will need additional parameters: N, effect size, alpha, power, etc.

Is there any other measure of cancer available? Stage, severity, biochemical assay, time to diagnosis, survival time, etc.? Why do you want to perform a logistic regression?

What covariates are available? What is known about potential confounders?

What is the nature of the study?

Good luck,

Kevin

Kevin Viel Department of Epidemiology Rollins School of Public Health Emory University Atlanta, GA 30322


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