I am running a multilevel generalized linear analysis that looks as follows model All predictors have two levels except block and pulse , which are continuous. Arousal is a Likert scale with 9 points. I get this warning Warning message: In summary.clmm(model) : Variance-covariance matrix of the parameters is not defined I read this thread on the topic: https://github.com/runehaubo/ordinal/issues/9 I ran this code: xtabs(~condition+age_group+block_number+pulse, Ratings_final) I have lots of 0s. Based on the thread, I should interpret this as indicating that the predictors are singularly bound to each other. Is this really the case? If I run a linear mixed model instead, it gets no error. Could someone help me understand this output or what is going on?

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