|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|
|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:
> 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.
> J S Huang
> fax 1-515-557-2422
> >>> wraong <firstname.lastname@example.org> 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
> and a group of patients without the specified outcome (controls).
> Investigators then compare the cases and the controls to determine
> 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
> > 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.
> > in
> > the above condition, I don't think it's correct to just set
> > of
> > exposure in control group as 0.25.
> > So I need your help on how to solve such problem.
> > Thanks.