Others have explained why R gives a different answer based on a different approximation, but if you want to get the same answer as the book/minitab/... for your own understanding (or so the grader doesn't get confused by superior answers, or other reasons) here is one way to do it:
> x <- c( rep(1,202), rep(0, 1010-202) ) > p <- 202/1010 > sd <- sqrt( p*(1-p) ) > > library(TeachingDemos) > z.test( x, 0.5, sd ) One Sample z-test data: x z = -23.8354, n = 1010.000, Std. Dev. = 0.400, Std. Dev. of the sample mean = 0.013, p-value < 2.2e-16 alternative hypothesis: true mean is not equal to 0.5 95 percent confidence interval: 0.1753312 0.2246688 sample estimates: mean of x 0.2 Which matches the others you reported below. -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Jack Sofsky > Sent: Sunday, July 17, 2011 10:27 AM > To: r-help@r-project.org > Subject: [R] ?Accuracy of prop.test > > I have just joined this list (and just started using R), so please > excuse any etiquette breaches as I do not yet have a feel for how the > list operates. > > I am in the process of teaching myself statistics using R as my utility > as my ultimate goals cannot be satisfied by Excel or any of the plug- > ins > I could afford. > > I am currently looking at chap12 page 552 of Weiss's Introductory > Statistics 9th edition. Example 12.5 demonstrates using "Technology" > to > obtain a One-Proportion z-Interval. > > n=202 > x=1010 > confidence interval = .95. > > Answer given by Minitab > 0.175331, .224669 > Answer given by TI-83/84 > .17533, .22467 > Answer given by Weiss's Excel Plug-in > 0.175 < p < 0.225 > > Here is what I got with R > prop.test(202,1010,correct="FALSE") > > 1-sample proportions test without continuity correction > > data: 202 out of 1010, null probability 0.5 > X-squared = 363.6, df = 1, p-value < 2.2e-16 > alternative hypothesis: true p is not equal to 0.5 > 95 percent confidence interval: > 0.1764885 0.2257849 > sample estimates: > p > 0.2 > > I'm also getting slight differences in the answers for exercises and > find this disconcerting. > > Why are these differences present (or am I doing something wrong)? > > Jack > > ______________________________________________ > R-help@r-project.org 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@r-project.org 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.