qqnorm(), is it "backwards"?
On Thu, 21 Sep 2000 17:10:27 -0500 (CDT), Pete Hurd
<phurd at uts.cc.utexas.edu> wrote:
Hello R friends, I'm wondering why I get funny qqnorm() results. It seems that they should all be reflected in the normal qqline().
I think the problem is that there are several different conventions for drawing these. Some people put the theoretical quantiles on the x axis (like R does), some put them on the y axis. I think some people plot probabilities rather than quantiles. Some books (e.g. if I recall correctly, Montgomery and Peck's regression text) even label things one way and draw them another. As far as I can tell, R is doing things correctly according to the convention it uses. That convention makes sense to me, too: like all plots of residuals, the residuals are shown on the y axis, the "fixed things" on the x axis. For a sample like runif(1000), the plot curves up at the left and down at the right, because the uniform distribution doesn't take such extreme values as the normal distribution does. Duncan Murdoch -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._