[R] qqplot

[David Winsemius]

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