I would normally expect to run a repeated-measures ANOVA in R (using aov wherein SCORE~TREATMENT*TYPE+Error(SUBJECT/(TREATMENT*TYPE))). However, there is a peculiarity of the design that I think may be causing problems. Namely that the factors are not fully crossed at the subject level. The issue appears to be that each subject experienced either of the following:

*Treatment A is Visual AND Treatment B is Auditory*

OR

*Treatment A is Auditory AND Treatment B is Visual*

That is, each subject experienced BOTH levels of Treatment (A and B), but only 1 level of Treatment Type for each Treatment, and always a different level of Treatment Type for each Intervention (Auditory for one and Visual for the other, or vice versa).

Ostensibly, the study is focused on the effects of Treatment, Treatment Type, and whether they interact.

In general this is a "within-subjects" design but I keep getting the "error model is singular" message when running a repeated-measures ANOVA using aov, and the sample sizes (for Treatment A-Auditory, Treatment A-Visual, Treatment B-Auditory, Treatment B-Visual) are equal. Maybe I'm off-base here and should focus on a different aspect. Thanks in advance for any advice!