Date:         Thu, 13 Oct 2011 15:29:05 -0400
Reply-To:     William Shakespeare <shakespeare_1040@HOTMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         William Shakespeare <shakespeare_1040@HOTMAIL.COM>
Subject:      Re: Pilot study

This will be retrospective in nature using data already collected.  The
questions I'm addressing all require logistic regression.  I need to make
sure I have enough cases to adequately power my study but coming up with
the inputs for the sample size calculation is difficult.  If this were
prospective I'd pilot to obtain the inputs.  Due to the retrospective
nature of the present study the only way I could "pilot" it is to use the
existing data.  I don't know if that's appropriate.

On Thu, 13 Oct 2011 10:27:15 -0700, Fareeza Khurshed <fkhurshed@GMAIL.COM>
wrote:

>Is it going to be a prospective study or a retrospective where you use
info
>from the db?
>
>On Thu, Oct 13, 2011 at 7:19 AM, William Shakespeare <
>shakespeare_1040@hotmail.com> wrote:
>
>> I have a large database (>100k subjects) which I'm going to use to
answer
>> several research questions.  Normally, with a prospective study I'd run
a
>> pilot to obtain the necessary data for sample size calculation.
However,
>> that's not possible here. Would it be acceptable to draw a sample from
my
>> database and derive pilot data from it as long as I exclude all those
data
>> from subsequent analyses?
>>