[R] Normal probability plot examples for Wikipedia (was "qqnorm with histogram?")

[Charles Berry]

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