Date: Mon, 17 Nov 2008 11:44:28 -0600
Reply-To: Suhong Tong <sophidt@HOTMAIL.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Suhong Tong <sophidt@HOTMAIL.COM>
Subject: Re: Urgent help with power related for binomial proportion
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Thank you, Robin.
I tested and the numbers came out make sense to me. You saved my day!
To: sophiDT@HOTMAIL.COMCC: SAS-L@LISTSERV.UGA.EDUSubject: Re: Urgent help with power related for binomial proportionFrom: firstname.lastname@example.orgDate: Mon, 17 Nov 2008 09:06:45 -0600Sophia, 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 <sophiDT@HOTMAIL.COM> Sent by: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
11/16/2008 05:17 PM
Please respond toSophia Tong <sophiDT@HOTMAIL.COM>
Urgent help with power related for binomial proportion
Dear SAS -L listers,I am trying to calculate minimum detectable difference in a proposed studyto cpmare with historical data. The sample size, proportion of historicaldata are known (n1 and P1 are know known). Power and Alpha are arbitarilydecided as 0.8 and 0.025, sample size was also proposed for differentnumbers ( 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 andgive it up after finding it's beyond my knowledge.Does anyone know how to do it in SAS, will PROC POWER do it? Or anyformular people have already figured it out?My deadline is tomorow, you help is greatly appreciated.ThanksSophia
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