My question is directly linked to the popular lmer cheat sheet. There was one situation that I didn't see mentioned in that cheat sheet and I wanted to know if it was a valid scenario or something that has no interpretation? I am still a neophyte to the complex world of mixed modelling so forgive me if the formulation does not make sense.
I wanted to know if:
V1 ~ V2 + (V3|V4)
Was correctly stated model. Particularly I'm interested in how I interpret the random effect associated with V3. In the usual case the model would have been specified in the form V1 ~ V2 + V3 + (V3|V4). And in this case the random effect on V3 is measuring how much it deviates from the global effect of V3 which would be the fixed slope effect. I was wondering if in the scenario I stated above would the interpretation of V3 be similar but this time there is no "global effect" estimated in the model and only the variation from V3?
V3slope of zero and the subject-level slopes are centered around that. Usually, this is not considered sensible. You should always include a corresponding fixed effect if you include a random effect. – Roland Aug 22 '23 at 05:51