More:

When the t-stat is > 0 should I use 'pt' differently?

I have been checking my results and (except for the example I posted) all
the inconsistencies occur when t>0

Worik

On Thu, Jun 17, 2010 at 10:30 AM, Worik R <worikr@gmail.com> wrote:

> I have two pairs of related vectors
> x1,y1
>
> and
>
> x2,y2
>
> I wish to do a test for differences in means of x1 and y1, ditto x2 and y2.
>
> I am getting odd results.  I am not sure I am using 'pt' properly...
>
> I have not included the raw vectors as they are long.  I am interested if I
> am using R properly...
>
> > c(length(x1), length(y1), length(x2), length(y2))
> [1] 3436 1619 2677 2378
>
>
> First where the T-stat and the DF do not give the same result as 't.test'
> when passed into 'pt'
>
> > t.1 <- t.test(x1, y1)
> > 2 * pt(t.1$statistic, t.1$parameter)
>        t
> 1.353946
> > t.1$p.value
> [1] 0.646054
>
> I would have thought these would have been the same.  Like below....
>
> > t.2 <- t.test(x2, y2)
> > 2 * pt(t.2$statistic, t.2$parameter)
>         t
> 0.8679732
> > t.2$p.value
> [1] 0.8679732
>
> This is what I expect.
>
> clearly I misunderstand some thing.  What is it?
>
> cheers
> Worik
>

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