Helmert Contrasts
First off, I'd like to say "thank-you"! JASP is as easy to use as SuperANOVA , and SPSS is still as dreadful to use as when I first started using it on a VAX system 25 years ago
My big question has to do with Helmert contrasts. The results I'm getting in JASP are not matching the results I'm getting in SPSS.
JASP:
Comparison Estimate SE t p
L1 - L2, L3, L4 0.488 0.148 3.300 0.002
L2 - L3, L4 0.101 0.139 0.725 0.473
L3 - L4 0.008 0.121 0.064 0.950
SPSS:
Contrast Type3 SS df MeanSquare F Sig.
Source Level 1 vs. Later 5.497 1 5.497 5.833 .032
Level 2 vs. Later 0.299 1 0.299 1.759 .209
Level 3 vs. Level 4 0.003 1 0.003 0.005 .946
Error Level 1 vs. Later 11.213 12 0.934
Level 2 vs. Later 2.036 12 0.170
Level 3 vs. Level 4 7.772 12 0.643
This is a repeated-measures anova with 1 IV and 4 levels. I’ve double checked both the descriptives and the omnibus ANOVA, and both JASP and SPSS give the same results, with the only difference being the Helmert contrasts (hand-coded Helmert contrasts give the same result as the built-in contrast).
Comments
I went and did the contrasts by hand, and came up with the same answers as JASP. Out of curiosity, I tried doing the contacts using a series of students-t tests in Excel, and came up with the same answer as SPSS.
I think I had a similar issue back in the days of SuperAnova: SuperAnova calculated contrasts correctly, but SPSS did not.
Hi Matt,
JASP borrows most of its functionality from R packages. I have not yet gotten a response from the person who implemented this in JASP, but I'm certain this comes from an R package. And it's nice to hear that it corresponds to what you did by hand.
Cheers,
E.J.