Hi, In addition to Terry’s great comments below, as this subject has come up frequently over the years, there is also a great document by Bill Venables that is valuable reading:
Exegeses on Linear Models http://www.stats.ox.ac.uk/pub/MASS3/Exegeses.pdf Regards, Marc Schwartz > On Jul 22, 2015, at 8:15 AM, Therneau, Terry M., Ph.D. <thern...@mayo.edu> > wrote: > > "Type III" is a peculiarity of SAS, which has taken root in the world. There > are 3 main questions wrt to it: > > 1. How to compute it (outside of SAS). There is a trick using > contr.treatment coding that works if the design has no missing factor > combinations, your post has a link to such a description. The SAS > documentation is very obtuse, thus almost no one knows how to compute the > general case. > > 2. What is it? It is a population average. The predicted average treatment > effect in a balanced population-- one where all the factor combinations > appeared the same number of times. One way to compute 'type 3' is to create > such a data set, get all the predicted values, and then take the average > prediction for treatment A, average for treatment B, average for C, ... and > test "are these averages the same". The algorithm of #1 above leads to > another explanation which is a false trail, in my opinion. > > 3. Should you ever use it? No. There is a very strong inverse correlation > between "understand what it really is" and "recommend its use". Stephen > Senn has written very intellgently on the issues. > > Terry Therneau > > > On 07/22/2015 05:00 AM, r-help-requ...@r-project.org wrote: >> Dear Michael, >> thanks a lot. I am studying the marginality and I came across to this post: >> >> http://www.ats.ucla.edu/stat/r/faq/type3.htm >> >> Do you think that the procedure there described is the right one to solve my >> problem? >> >> Would you have any other online resources to suggest especially dealing with >> R? >> >> My department does not have a statician, so I have to find a solution with >> my own capacities. >> >> Thanks in advance >> >> Angelo ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
