Hi Murli, First of all, regarding prop.test, you made a typo: you should have used prop.test(c(69,90),c(300,300)) which gives you the squared value of 3.4228, and it's square root is 1.85 which is not too far from 1.94.
I would use Fisher Exact Test (fisher.test). Two sided test has a p-value of 0.06411 so you do not reject H0, One sided test (i.e. H1 is that the first probability of success is smaller than the second) has a p-value of 0.03206, so you reject H0 (with 95% confidence level). You get similar results with two-sided and one-sided t-test. Moshe. P.S. if you use paired t-test you get nonsense since it uses pairwise differences, and in your case only 21 of 300 differences are non-zero! --- "Nair, Murlidharan T" <[EMAIL PROTECTED]> wrote: > n=300 > 30% taking A relief from pain > 23% taking B relief from pain > Question; If there is no difference are we likely to > get a 7% difference? > > Hypothesis > H0: p1-p2=0 > H1: p1-p2!=0 (not equal to) > > 1>Weighed average of two sample proportion > 300(0.30)+300(0.23) > ------------------- = 0.265 > 300+300 > 2>Std Error estimate of the difference between two > independent proportions > sqrt((0.265 *0.735)*((1/300)+(1/300))) = > 0.03603 > > 3>Evaluation of the difference between sample > proportion as a deviation from the hypothesized > difference of zero > ((0.30-0.23)-(0))/0.03603 = 1.94 > > > z did not approach 1.96 hence H0 is not rejected. > > This is what I was trying to do using prop.test. > > prop.test(c(30,23),c(300,300)) > > What function should I use? > > > -----Original Message----- > From: [EMAIL PROTECTED] on behalf of > Nordlund, Dan (DSHS/RDA) > Sent: Thu 8/9/2007 1:26 PM > To: r-help@stat.math.ethz.ch > Subject: Re: [R] small sample techniques > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] On > Behalf Of Nair, > > Murlidharan T > > Sent: Thursday, August 09, 2007 9:19 AM > > To: Moshe Olshansky; Rolf Turner; > r-help@stat.math.ethz.ch > > Subject: Re: [R] small sample techniques > > > > Thanks, that discussion was helpful. Well, I have > another question > > I am comparing two proportions for its deviation > from the hypothesized > > difference of zero. My manually calculated z ratio > is 1.94. > > But, when I calculate it using prop.test, it uses > Pearson's > > chi-squared > > test and the X-squared value that it gives it > 0.74. Is there > > a function > > in R where I can calculate the z ratio? Which is > > > > > > ('p1-'p2)-(p1-p2) > > Z= ---------------- > > S > > ('p1-'p2) > > > > Where S is the standard error estimate of the > difference between two > > independent proportions > > > > Dummy example > > This is how I use it > > prop.test(c(30,23),c(300,300)) > > > > > > Cheers../Murli > > > > > > Murli, > > I think you need to recheck you computations. You > can run a t-test on your data in a variety of ways. > Here is one: > > > x<-c(rep(1,30),rep(0,270)) > > y<-c(rep(1,23),rep(0,277)) > > t.test(x,y) > > Welch Two Sample t-test > > data: x and y > t = 1.0062, df = 589.583, p-value = 0.3147 > alternative hypothesis: true difference in means is > not equal to 0 > 95 percent confidence interval: > -0.02221086 0.06887752 > sample estimates: > mean of x mean of y > 0.10000000 0.07666667 > > Hope this is helpful, > > Dan > > Daniel J. Nordlund > Research and Data Analysis > Washington State Department of Social and Health > Services > Olympia, WA 98504-5204 > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, > reproducible code. > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, > reproducible code. > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.