Peter, I am asked to show seasonal effects vs a general averaged level without any seasonal effects. That's why contr.sum and not treatment. The estimates show that some coefs are not stat different from 0, which is also the enforced total average. So, my understanding of model selection leads me to force certain seasons to be zero.
For example: Y= a0 + b1 + Xb | factor=1 Y= a0 +Xb | factor=2 Y= a0 + b2 + Xb | factor=3 b1+b2=0 | which in this case means b1=-b2 but with more levels not necessarily Stephen Bond | -----Original Message----- From: Peter Dalgaard [mailto:pda...@gmail.com] Sent: Thursday, July 08, 2010 4:09 AM To: Bond, Stephen Cc: r-help@r-project.org Subject: Re: [R] forcing a zero level in contr.sum Bond, Stephen wrote: > I need to use contr.sum and observe that some levels are not > statistically different from the overall mean of zero. What is the > proper way of forcing the zero estimate? It seems the column > corresponding to that level should become a column of zeros. Is there > a way to achieve that without me constructing the design matrix? As Berwin (indirectly) points out, you probably overlooked the how.many argument to C(). However, are you _sure_ that you want to do this? This is like testing that one treatment is exactly equal to the average of all other treatments, which is a rather strange hypothesis. -- Peter Dalgaard Center for Statistics, Copenhagen Business School Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-help@r-project.org mailing list 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.
