qqplot

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

mailing list

reproducible code.