[R] probability-probability plot
Spencer Graves
spencer.graves at pdf.com
Sun Jul 3 05:33:20 CEST 2005
There are PP plots and QQ plots. I've tried PP plots and didn't get
much from them. The normal QQ plot [qqnorm, in R], however, I use for
all kinds of things. In a data mining situation, I'll get, e.g., 500
p.values, all uniformily distributed under the null hypothesis. I'll
transform that null distribution to N(0, 1) with qnorm(p.values) and make
qqnorm(qnorm(p.values), datax=TRUE).
I may be chastised severely by Tukeyites for "datax=TRUE", but the
human eye can decode a 45 degree angle easier than any other angle other
than horizontal or vertical. If you have a couple of mild outliers with
a typical aspect ratio of the plot, the "datax=TRUE" option will make
the line moderately close to 45 degrees.
spencer graves
Jonathan Baron wrote:
> On 07/02/05 15:41, Yulei He wrote:
> Hi, there.
>
> Is there any function in R to plot the probability-probability plot (PP
> plot)? Suppose I am testing some data against normal.
>
> qqnorm might be what you want, or lead to it.
>
--
Spencer Graves, PhD
Senior Development Engineer
PDF Solutions, Inc.
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spencer.graves at pdf.com
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