Date:         Mon, 8 May 2006 13:06:07 -0400
Reply-To:     Susie Li <Susie.Li@TVGUIDE.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Susie Li <Susie.Li@TVGUIDE.COM>
Subject:      Re: help on power calculation
Content-Type: text/plain; charset="us-ascii"

Isn't that similar to a logistic regression problem, where your
dependent variable is either the event (cases - with the outcome) or
non-event (controls - without the outcome)?

Maybe you want to add a segment variable (the upper quartile, lower
quartile that people belong to) in a logistic model form /multiple
regression model form specified to SAS PROC POWER for your power
calculation.

Susie Li
TV Guide
1211 Avenue of the Americas
New York, NY 10036
Tel 212.852.7453
Email susie.li@tvguide.com

-----Original Message-----
From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of
wraong
Sent: Monday, May 08, 2006 12:39 PM
To: SAS-L@LISTSERV.UGA.EDU
Subject: Re: help on power calculation

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.
>