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Topic: Type I and III Sum of Squares? Help
Replies: 1   Last Post: Jun 17, 1996 3:20 AM

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Laura Hamilton

Posts: 2
Registered: 12/18/04
Re: Type I and III Sum of Squares? Help
Posted: Jun 17, 1996 3:20 AM
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Chem and Soil Science Dept Mac Computer wrote:
> Hi,
> I am performing ANOVA on a data set. In SAS, the procedure I am using
> generates Type I and Type III sums of squares. How will I know which one
> to use? the "p" values generated are different between the two types.
> Thanks Very Much.
> Andrew W.
> Aweatherbee@cox.nsac.ns.caIt depends on what you are trying to do with the ANOVA. The Type I Sum

of Squares is a Sequential Sum of Squares giving the significance of the
added variable, given the variables added before it, whereas the Type III
Sum of Squares gives the significance of the variable given ALL other
variables in the model. Should be careful when looking at Type III
p-values of t-tests. Eliminating variables based on t-test may not be
the correct thing to do.

Good luck!


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