# [R] Homework help: Is this how CI using t dist are constructed?

Zembower, Kevin kzembowe at jhuccp.org
Tue Oct 30 21:24:54 CET 2007

```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:
> 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?

-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

```