Hi math people.

I'm in the process of analyzing some data that I collected through an experiment. The data are (somewhat) normally distributed and I represent the different data-sets using boxplot, to provide an easy way of visually comparing the mean between the data-sets and the change in the variance.

In Matlab as default, the whiskers are used to represent all samples lying within 1.5 times the IQR. According to Wikipedia on the boxplot, this is one of several way of using the whiskers. My question is simple why? What special significance does 1.5 times IQR have? Why not e.g. three times sigma?

(NB: I wanted to add the tags "matlab" and "boxplot", but I'm unable to create new tags.)