Date:         Tue, 26 Aug 2008 07:49:51 -0700
Reply-To:     Jeff <jeffrey.m.allard@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Jeff <jeffrey.m.allard@GMAIL.COM>
Organization: http://groups.google.com
Subject:      Re: Proc Power
Comments: To: sas-l@uga.edu
Content-Type: text/plain; charset=ISO-8859-1

On Aug 26, 9:44 am, rh...@UNMC.EDU (Robin R High) wrote:
> It appears to allow you to specify a difference in the two proportions
> other than 0 for a null hypothesis
>
> * e.g., Test H0: p1 - p2 = .01 ;
>
> PROC POWER;
> TWOSAMPLEFREQ
>    TEST = pchi
>    SIDES = 2
>    ALPHA = .05
>    GROUPPROPORTIONS = (.45 .25)
>    NULLPROPORTIONDIFF=.01      /* need to enter TEST=pchi and either
> GROUPPROPORTIONS or PROPORTIONDIFF options */
>    NTOTAL = 100
>    POWER = .
> ;
> RUN;
>
> Robin High
> UNMC
>
> Bminer <b_mi...@LIVE.COM>
> Sent by: "SAS(r) Discussion" <SA...@LISTSERV.UGA.EDU>
> 08/25/2008 08:20 PM
> Please respond to
> Bminer <b_mi...@LIVE.COM>
>
> To
> SA...@LISTSERV.UGA.EDU
> cc
>
> Subject
> Proc Power
>
> If anyone has experience with Proc power:
>
> What does NULLPROPORTIONDIFF do exactly?
>
> Thanks
>
> brian

Hi Robin-

Am I alone in often finding SAS documentation really lacking? It is a
struggle to figure out what does what.

So this begs the question about the difference between PROPORTIONDIFF
and NULLPROPORTIONDIFF?

I would have thought that GROUPPROPORTIONS = (.45 .25)
would imply H0: .45 -.25 = 0.15 or a proportion difference
(PROPORTIONDIFF) in the null of 0.15.

But I do see that SAS uses p2-p1 in PROPORTIONDIFF. So I find that

GROUPPROPORTIONS = (.45 .25)

is the same as:

refproportion=  0.45
PROPORTIONDIFF= -0.25

Am I missing something?