I am running an ordinal regression for an experiment I have conducted, where the DV is ratings on a 5-point scale, and the predictors are the type of item, the type of participant (native speaker/L2/heritage) and the task (there were two tasks, both targeting the same type of linguistic phenomenon). I want to add random effects for participant and for item. I added an intercept for item
The problem: How to add the random effect for participant? There were different lists in the experiment, meaning - every participant only saw a subset of all items, no participant saw all items. I feel that this means that I cannot just add an intercept for participant, but have to somehow use different syntax to reflect the fact that each participant only saw a subset of the items.
There isn't a column/variable for the list number, so I cannot use participant as a variable nested in that.
How should I add a participant random effect?