Lisa Winer asks: > >First of all, does anyone know why it is customary to multiply 1.5*IQR in >order to find outliers? In particular, why is it 1.5 and not, for example, >2? >
The "official" answer from John Tukey (when I asked) is: because 1 is too small and 2 is too large.
There is a paper by Hoaglin and Ygelevich (sp?) in which they did some simulations and showed that the outlier rule is really quite good across a pretty wide array of distributions. I don't know the full reference.