z_scored_mlm_categorical: Z-scored for multilevel analyses
Description
This is a specialized function for mean centering categorical variables. There are two cases where this function should be used instead of the generic `center_mlm`.
1. This function should be used when you need group mean centering for non-dummy-coded variables at L1. Variables at L2 are always dummy-coded as they represent the percentage of subjects in that group.
2. This function should be used whenever you want to z-score the aggregated L2 means
An object of the same type as .data. The output has the following properties:
1. Columns from .data will be preserved
2. Columns with L1 scores that are group-mean centered
3. Columns with L2 aggregated means (i.e., percentage) that are z-scored
Arguments
data
A data.frame or a data.frame extension (e.g. a tibble).
cols
Dummy-coded or effect-coded columns for group-mean centering. Support `dplyr::dplyr_tidy_select` options.
dummy_coded
Dummy-coded variables (cannot be effect-coded) for L2 aggregated means. Support `dplyr::dplyr_tidy_select` options.
group
the grouping variable. Must be character
keep_original
default is `FALSE`. Set to `TRUE` to keep original columns