```Date: Tue, 26 Aug 2008 07:49:51 -0700 Reply-To: Jeff Sender: "SAS(r) Discussion" From: Jeff 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 > Sent by: "SAS(r) Discussion" > 08/25/2008 08:20 PM > Please respond to > Bminer > > 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? ```

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