[R] Normal probability plot examples for Wikipedia (was "qqnorm with histogram?")
Charles Berry
ccberry at ucsd.edu
Mon Aug 4 22:34:15 CEST 2014
Spencer Graves <spencer.graves <at> structuremonitoring.com> writes:
>
> Hi, Jim et al.:
>
> Thanks for the reply, Jim.
>
> What are your favorite examples using normal probability plots to
> identify outliers, skewness, kurtosis, mixtures, and the need for
> transformations in plots of raw data and residuals from model fits -- or
> using half-normal plots with estimated parameters?
>
Not sure I have a *favorite*, but the so-called "Fisher's iris data"
provide an illustration of an obvious mixture and the value of conditioning.
Try:
qqnorm(iris$Petal.Length,col=as.numeric(iris$Species))
qqnorm(residuals(lm(Petal.Length~Species,iris)))
As a bonus, you can reference this pretty page:
http://en.wikipedia.org/wiki/Iris_%28plant%29
where the contributions of the iris to water purification, art, and
symbolism are noted.
Maybe a section on the iris in statistics... ;-)
HTH,
Chuck
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