When only one variable in a multilevel model is of interest (all of the other variables are treated as nuisance parameters), and we wish to estimate between- and within-effects, should we only center the variable of interest for interpretability? Or should we still center all other variables and just omit reporting their associated model output? (Keeping things simple here and not referring to the type of centering, what level the other variables are at, etc. to focus specifically on my question of whether we center only the substantive variable of interest or all variables included in the model).