Doing: > t.test(x)
Will give the same CI (among other things), but it is good to do it the long way a couple of times to make sure that you understand what the canned approach is doing (but from now on you can use the t.test function). Also just as a minor terminology correction, usually alpha would be 0.05 from your example, what you have as 0.95 is the confidence level (1-alpha). Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare [EMAIL PROTECTED] (801) 408-8111 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Zembower, Kevin > Sent: Tuesday, October 30, 2007 2:25 PM > To: r-help@r-project.org > Subject: [R] Homework help: Is this how CI using t dist are > constructed? > > I'm trying to replicate some of the examples from my textbook > in R (my text uses Minitab). In this problem, I'm trying to > construct a 95% confidence interval for these distance > measurements [1]: > > > # Case Study 7.4.1, p. 483 > > x <- scan() > 1: 62 52 68 23 34 45 27 42 83 56 40 > 12: > Read 11 items > > alpha<-.95 > > mean(x) + qt(c((1-alpha)/2, 1-((1-alpha)/2)), > df=length(x)-1) * sd(x) > / sqrt(length(x)) > [1] 36.21420 60.51307 > > > > Are confidence intervals with the t distribution constructed > using this type of equation, or am I overlooking a more > concise, 'canned' approach that's already been programmed? > Any suggestions on simplifying this? > > Thanks for all your advice and help. > > -Kevin > > [1] An Introduction to Mathematical Statistics and its > Applications, fourth ed., Larsen and Marx. > > Kevin Zembower > Internet Services Group manager > Center for Communication Programs > Bloomberg School of Public Health > Johns Hopkins University > 111 Market Place, Suite 310 > Baltimore, Maryland 21202 > 410-659-6139 > > ______________________________________________ > 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.
