Hi---I am trying to convert examples for my stats class from SPSS to R. The within and between group Sums of Squares (SS) are very different when I compare the SPSS results to R. For example, Between Groups in SPSS is 116.7 and the Within Groups is 140.6. In R, I use the function "aov" which calculates "Group SS" as 16.07 and residuals SS is 242.2 What is going on? I double/triple checked and I am using the same data. Help!
Hi, welome to the forum.
I know I've seen this discussed three or four years ago before but here in a quick AI response for some problems.
ANOVA results often differ between R and SPSS due to default Sum of Squares (SS) types: R (`aov` or `anova` ) uses **Type I (sequential)** , while SPSS uses **Type III (marginal)** by default.
For unbalanced data, this causes differences in SS, F-values, and
-values. Use `car::Anova(model, type="III")` in R for matching SPSS.
Many thanks! I figured it had something to do with the "type" but wasn't sure...or how to fix it. Thank you!