I use QQ plots extensively to analyze lognormal data. Unfortunately the Grapher implementation will not allow for this. As I understand it, Grapher is using a function to interpolate one of the quantile sets. It would be nice if there was an option to use straight quantiletoquantile matching, which would allow for a QQ plot with lognormal axes.

Hello Fred,
This is not correct. Grapher does not interpolate either of the quantile sets, it plots the same quantile in one set against that same quantile in the other set. From the QQ Plots and Normal QQ Plots page in the help:
A QQ plot is a type of probability plot which compares the probability distribution of two data sets by plotting their quantiles against each other. Each point plotted on the QQ plot represents the same quantile in each data set. If the two distributions being compared have similar distributions, the points will approximately lie on the line y=x. If the distributions are linearly related, the points will lie on a line, but not necessarily the y=x line.
If you have a QQ plot with log axes that is not displaying as expected, you're welcome to send it to graphersupport@goldensoftware.com and we will take a look.
Thanks,
Leslie
Please sign in to leave a comment.
Comments
1 comment