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  • $\begingroup$ How do you define a slope for variable group which is a categorical variable? $\endgroup$ Commented Nov 28, 2023 at 13:34
  • $\begingroup$ Sorry but I dont understand the issue. I've seen plenty of examples with 2 categories as fixed variables (example: ed.ac.uk/biomedical-sciences/…) $\endgroup$ Commented Nov 28, 2023 at 13:39
  • $\begingroup$ Let me clarify, how do you define a random slope for group? $\endgroup$ Commented Nov 28, 2023 at 13:43
  • $\begingroup$ Sorry, this might all be going over my head, but isn't that the case every time you want to evaluate the extent onto which a covariate may have, together with a predictor, on an outcome? $\endgroup$ Commented Nov 28, 2023 at 16:05
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    $\begingroup$ There's nothing wrong with your code as such. You can very well include a random slope of a categorical predictor, though it may feel strange to call it a slope because what you get is a contrast estimate for each subject. I'm not sure if the fact that you only have 2 observations per subject causes some issues though (in the example you link, they had several observations for each modality per subject). $\endgroup$ Commented Nov 29, 2023 at 16:04