[R] Homework help: Is this how CI using t dist are constructed?
Greg Snow
Greg.Snow at intermountainmail.org
Wed Oct 31 16:06:38 CET 2007
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
greg.snow at intermountainmail.org
(801) 408-8111
> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of Zembower, Kevin
> Sent: Tuesday, October 30, 2007 2:25 PM
> To: r-help at 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
>
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