[R] qqplot

[carol white]

So the conclusion is that abline(0,1) should always be used and if it doesn't go through the qqplot, the two distributions are not similar?

Thanks

--- On Mon, 11/2/09, Yihui Xie <xieyihui at gmail.com> wrote:

> From: Yihui Xie <xieyihui at gmail.com>
> Subject: Re: [R] qqplot
> To: "carol white" <wht_crl at yahoo.com>
> Cc: "David Winsemius" <dwinsemius at comcast.net>, r-help at stat.math.ethz.ch
> Date: Monday, November 2, 2009, 8:42 AM
> abline(0,1) is somewhere in the
> upper-left corner which you are unable
> to see. At least the first distribution seems to have a
> larger mean
> than the second one (i.e. they are not the same
> distribution).
> 
> Regards,
> Yihui
> --
> Yihui Xie <xieyihui at gmail.com>
> Phone: 515-294-6609 Web: http://yihui.name
> Department of Statistics, Iowa State University
> 3211 Snedecor Hall, Ames, IA
> 
> 
> 
> On Mon, Nov 2, 2009 at 10:33 AM, carol white <wht_crl at yahoo.com>
> wrote:
> > if I have the two following matrices, abline(0,1)
> doesn't go through. QQplot is attached.
> >
> >            [,1]     [,2]     [,3]     [,4]
>     [,5]
> >  2.149644 1.992864 3.346375 2.793511 3.428230
> >  1.100762 2.152981 2.735401 2.175185 3.323058
> > 1.212406 2.131813 2.672598 2.389996 3.242490
> > 1.183770 1.908633 2.661237 2.590545 2.906059
> >  1.665190 1.778923 2.636062 2.475619 4.013407
> >
> >
> >    0.601   0.083   0.520    0.920  -0.007
> >   -0.778   0.427  -0.605   -0.066  -0.283
> >  -0.599   0.348  -0.693    0.284  -0.436
> >   -0.519   0.081  -0.590    0.678  -1.095
> >    0.009  -0.253  -0.940    0.526   1.623
> >
> >
> > --- On Mon, 11/2/09, David Winsemius <dwinsemius at comcast.net>
> wrote:
> >
> >> From: David Winsemius <dwinsemius at comcast.net>
> >> Subject: Re: [R] qqplot
> >> To: "carol white" <wht_crl at yahoo.com>
> >> Cc: r-help at stat.math.ethz.ch
> >> Date: Monday, November 2, 2009, 8:17 AM
> >>
> >> On Nov 2, 2009, at 10:40 AM, carol white wrote:
> >>
> >> > Hi,
> >> > We could use qqplot to see how two
> distributions are
> >> different from each other. To show better how they
> are
> >> different (departs from the straight line), how is
> it
> >> possible to plot the straight line that goes
> through them? I
> >> am looking for some thing like qqline for qqnorm.
> I thought
> >> of abline but how to determine the slope and
> intercept?
> >>
> >> I always assumed that the intercept was zero and
> the slope
> >> = unity.
> >>
> >>  y <- rt(200, df = 5)
> >>  qqnorm(y); qqline(y, col = 2)
> >>  qqplot(y, rt(300, df = 5))
> >>  abline(0, 1, col="red")
> >>
> >> I am open to education if that assumption is too
> >> simplistic, but you have not offered anything in
> the way of
> >> a counter-example.
> >>
> >> >
> >> ==
> >>
> >> David Winsemius, MD
> >> Heritage Laboratories
> >> West Hartford, CT
> >>
> >>
> >
> >
> >
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> >
> >
>