For the data structure, we are fitting the multilevel model to the data. Before fitting the model, we are eager to do bivariate analysis so that we can keep those independent variables in the multilevel model which has an association with the dependent variable. My question is that since in the multilevel model, there is a group variable where the data are nested within each group, do I need to create different bivariate table for each group? Or, will I create single bivariate table where group is an independent variable?
That is, for example, I have $x_1, x_2, x_3, x_4, x_5$ and group variables as independent variables. Here, group has three categories. If before fitting the multilevel model, I want to do bivariate analysis, will I do that analysis separately for thee categories of group variable, or there will be only one unified bivariate analysis where I will check association between group variable and dependent variable too?