[R] Homework help: Is this how CIs of normal distributions are computed?

[Nordlund, Dan (DSHS/RDA)]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Zembower, Kevin
> Sent: Wednesday, October 31, 2007 12:57 PM
> To: r-help at r-project.org
> Subject: [R] Homework help: Is this how CIs of normal 
> distributions are computed?
> 
> I'm looking for a function in R similar to t.test() which was 
> generously
> pointed out to me yesterday, but which can be used for normally
> distributed data.
> 
> To recap yesterday:
> > x <- scan()
> 1: 62 52 68 23 34 45 27 42 83 56 40
> 12: 
> Read 11 items
> > alpha<- .05
> > t.test(x)
> 
>         One Sample t-test
> 
> data:  x 
> t = 8.8696, df = 10, p-value = 4.717e-06
> alternative hypothesis: true mean is not equal to 0 
> 95 percent confidence interval:
>  36.21420 60.51307 
> sample estimates:
> mean of x 
>  48.36364 
> 
> What if I now mock-up my data for 100 trials:
> > x100<-sample(x, 100, replace=TRUE)
> 
> I think that I should be able to use a normal distribution, because of
> the n>30 rule-of-thumb.
> 
<<<snip>>>

You could probably use the Normal distribution as an approximation under these circumstances, but why would you when you have a more accurate CI using t.test?

Dan


Daniel J. Nordlund
Research and Data Analysis
Washington State Department of Social and Health Services
Olympia, WA  98504-5204