this link has group predictors :

https://widdowquinn.github.io/Teaching-Stan-Hierarchical-Modelling/11-group_level_predictors.html

it shows the group predictor “u” is the same length as the the number of observations N so all the rows from a county will have the same value. Is that the correct way to add a group predictor or should the group predictor be the same length as the group?

seems the group predictor is at the group level not the observation level so why have it at observation level?

And in this link 19.1.3 it states “we need only plunk the group-level `walk_score`

predictor directly into the `stan_glmer()`

formula. Since all listings in the same neighborhood share the same `walk_score`

, it is automatically recognized as a group-level predictor.”

Will stan glmet have the group predictor the length of data or length of the group levels?