Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
| From | Maarten Buis <maartenlbuis@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: van der Waerden transformation |
| Date | Fri, 13 Apr 2012 09:33:05 +0200 |
On Thu, Apr 12, 2012 at 7:01 PM, Austin Nichols <austinnichols@gmail.com> wrote: > Maarten-- > how about test scores? Why would you want to make up distances between ranks in test scores? I can see why many of these do not have a natural unit, so some form of standardization is called for, but that does not mean that they should be forced into a normal/Gaussian distribution. If you find considerable skewness in your raw scores, would the forced to be normal variable really be a better represenation of what you found? -- Maarten > > On Thu, Apr 12, 2012 at 12:42 PM, Maarten Buis <maartenlbuis@gmail.com> wrote: >> On Thu, Apr 12, 2012 at 6:11 PM, Scott Merryman wrote: >>> Isn't the van der Waerden transformation just inverse_normal(rank/(N +1)) ? >> >> That sounds like an awful idea. That way you are just "inventing" >> distances between ranks that have nothing to do with what you >> observed. If you (generally speaking, not Scott specifically) really >> want to get rid of the skewness that badly, than just use the >> percentile rank and be honest about the fact that you have thrown away >> the information on the distances between the ranks rather than making >> those distances up. In general, I would _not_ try to get rid of the >> skewness, but rather use it. If it is a dependent variable that might >> suggest a -glm- with maybe a log link function. If it is an >> independent variable it might suggest a non-linear effect possibly to >> be modeled with splines (see: -mkspline-). >> >> I would be interested to hear if someone knows of an application where >> this transformation would make some sense. I cannot imagine one, but >> that may just be due to my lack of imagination. >> >> -- Maarten > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ -- -------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany http://www.maartenbuis.nl -------------------------- * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/