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.