It is of note that the LME approach does not work when other explanatory variables (multiple groups, conditions, or quantitative covariates) are involved because (2a) or (2b) cannot be formulated due to the parameterization constraint through dummy coding. For instance, when there are two groups involved, the typical contrast coding for the two groups renders one dummy variable (e.g., the contrast of one group vs. the other when effect coding is adopted); however, such a coding strategy relies on the existence of an intercept in the model. If the two groups are coded by two indicator variables, the model matrix would become overparameterized.