```Date: Mon, 17 Nov 2008 09:06:45 -0600 Reply-To: Robin R High Sender: "SAS(r) Discussion" From: Robin R High Subject: Re: Urgent help with power related for binomial proportion Comments: To: Sophia Tong In-Reply-To: <200811162315.mAGBmJKU003090@malibu.cc.uga.edu> Content-Type: text/plain; charset="US-ASCII" Sophia, PROC POWER won't let you solve for "delta" directly with the known inputs, though with a bit of trial and repeated runs you can find a delta that matches the input data you have, that is run the following code by entering what you do know and modify the second value in the GROUPPROPORTIONS option - xxxx -- until the value for p2 gives you .8 power: PROC POWER; TWOSAMPLEFREQ TEST = pchi /*other options: fisher lrchi pchi*/ SIDES = 2 ALPHA = .025 GROUPPROPORTIONS = (p1 xxx) GROUPNS = (n1 n2) POWER = . ; RUN; suppose p1=.2, n1=85, n2=90, with the values for alpha and number of sides, then PROC POWER; TWOSAMPLEFREQ TEST = pchi /*fisher lrchi pchi*/ SIDES = 2 ALPHA = .025 GROUPPROPORTIONS = (.2 .4135) GROUPNS = (85 90) POWER = . ; RUN; Power here is close to .8, so delta would be .4135-.2 = .2135 Robin High UNMC Sophia Tong Sent by: "SAS(r) Discussion" 11/16/2008 05:17 PM Please respond to Sophia Tong To SAS-L@LISTSERV.UGA.EDU cc Subject Urgent help with power related for binomial proportion Dear SAS -L listers, I am trying to calculate minimum detectable difference in a proposed study to cpmare with historical data. The sample size, proportion of historical data are known (n1 and P1 are know known). Power and Alpha are arbitarily decided as 0.8 and 0.025, sample size was also proposed for different numbers ( so, n2, beta and alpha are all known). I need find delta. I was trying to derive delta from sample size formular in a textbook and give it up after finding it's beyond my knowledge. Does anyone know how to do it in SAS, will PROC POWER do it? Or any formular people have already figured it out? My deadline is tomorow, you help is greatly appreciated. Thanks Sophia ```

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