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Date:   Mon, 8 May 2006 14:41:59 -0400
Reply-To:   wraong <wrong.wang@GMAIL.COM>
Sender:   "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:   wraong <wrong.wang@GMAIL.COM>
Subject:   Re: help on power calculation
Comments:   To: Jiann-Shiun Huang <Jiann-Shiun.Huang@amerus.com>
In-Reply-To:   <s45f2edc.063@mail6.amerus.com>
Content-Type:   text/plain; charset=ISO-8859-1; format=flowed

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.

On 5/8/06, Jiann-Shiun Huang <Jiann-Shiun.Huang@amerus.com> wrote: > > Wrong: > > I suppose that it is a hypothesis testing. If so, what are your null > and alternative hypotheses? How are your groups, cases and controls, > were selected for the study? What is the variable of interest? If you > find more information related to this calculation, provide them too. > > Thanks, > > J S Huang > 1-515-557-3987 > fax 1-515-557-2422 > > >>> wraong <wrong.wang@gmail.com> 05/08/06 11:38 AM >>> > Thanks for your kind suggestion. > > *Case-control study* is a retrospective observational study in which > investigators identify a group of patients with a specified outcome > (cases) > and a group of patients without the specified outcome (controls). > Investigators then compare the cases and the controls to determine > possible > factors which can be linked to the outcome. > > > On 5/8/06, Jiann-Shiun Huang <Jiann-Shiun.Huang@amerus.com> wrote: > > > > Wrong: > > > > Is it possible we can describe in detail about case-control study so > > that people like me without knowledge in the study could give a shot > at > > your problem? > > > > J S Huang > > 1-515-557-3987 > > fax 1-515-557-2422 > > > > >>> Wrong Wang <wrong.wang@GMAIL.COM> 05/08/06 11:16 AM >>> > > Hi, all > > > > I am asked to do power calculation for a case-control study, the > > sample > > sizes are equal in the two groups. I will compare the upper quartile > > group > > to the lower quartile group. > > > > I know I can use proc power in SAS to calculate power for a normal > > case- > > control study, which given prevalence of exposure in control group. > But > > in > > the above condition, I don't think it's correct to just set > prevalence > > of > > exposure in control group as 0.25. > > > > So I need your help on how to solve such problem. > > > > Thanks. > > >


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