Hi Nadine,
The estimation issue is due to the non-sphericity correction. You need to make sure the Subject factor is set to Independent and the between-subject factor is also set to Independent. You may also need to set this for the within-subject factor, effectively switching the non-sphericity correction off. The non-sphericity correction can be problematic in these types of designs.
These issues (as well as the correct specification of contrasts in these designs) is covered in my paper: https://www.frontiersin.org/articles/10.3389/fnins.2019.00352/full
Make sure you have a look through this to make sure you understand how these designs work before going any further.
Best wishes,
Martyn
|