[R] 2 Sample Confidence Interval - Formatting Data?
Marc Schwartz
marc_schwartz at comcast.net
Wed Oct 10 01:27:32 CEST 2007
On Tue, 2007-10-09 at 18:37 -0400, Wayne Aldo Gavioli wrote:
>
> Hello all,
>
> I have to run a 2 Sample Confidence Interval on some data; the command for such
> intervals is "confint(...)", but in the help documentation it says that you
> need a "fitted model object" in order to run this command. What does that
> mean?
>
> The data is very small, it's:
>
> x=c(8,12,10,14,2,0,0)
> y=c(-6,0,1,2,-3,-4,2)
>
>
> and I want to be able to run a Confidence interval for the difference of two
> means (x-bar minus y-bar). Do I have to fit these two pieces of data into some
> kind of object?
>
>
> A little confused,
Try this, presuming that your data above are not paired:
> t.test(x, y)
Welch Two Sample t-test
data: x and y
t = 3.0621, df = 9.264, p-value = 0.01308
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
2.039893 13.388678
sample estimates:
mean of x mean of y
6.571429 -1.142857
See ?t.test for more information.
confint(), as per the top of help page which you were reading:
"Computes confidence intervals for one or more parameters in a fitted
model."
Said differently, it computes confidence intervals for the coefficients
in a linear model, not for the difference in means in a two sample test.
HTH,
Marc Schwartz
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