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1 total messages Started by Andrew Cuddon, Civil Postg. Wed, 15 Apr 1992 05:02
ANOVAs for Linear Regression - Q1
#213
Author: Andrew Cuddon, Civil Postg.
Date: Wed, 15 Apr 1992 05:02
25 lines
1593 bytes
Regards to all,
I would appreciate some feedback on a lack of understanding.

I have a situation where I would like to determine if a constant term 
is neccessary for my simple linear regression model. I have become rather
confused over how an analysis of variance table is calculated when a 
CONSTANT term is not included in a linear regression.

My model produces R2 value of 0.7 with the constant term being significantly 
different from zero at the 1% level. In the interests of simplifying the model 
I re-ran the regression without the constant term and noted an increase in R2 
to 0.9.

This was fine but I also noted that the REGRESSION SUM OF SQUARES in 
the ANOVA table increased from 14.6 up to 375.4. This was because the TOTAL 
SUM OF SQUARES increased from 20.4 up to 381.5. If the two models are from the 
same data set, how can the TSS be different in each case? I believe this may 
be something to do with correcting for the mean but I don't really understand 
what is going on here.

Thanks in advance,
=============================
Andrew Cuddon
CUDDON@ENG2.ENG.MONASH.EDU.AU
=============================
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