My thesis is the impact of labor cross-regional mobility on income. The explanatory variable “cross-regional mobility” is divided into four categories: no cross-regional, cross-regional and county-level flows, cross-prefecture-level flows, and inter-provincial flows. The control variables include variables at the local level, such as GDP, industrial structure, and so on. Does this situation require a layered model? When I look at a teacher, he says that you need to use a layered model, but I think my explanatory variables and the variables being interpreted are at the same level, or if the model contains higher-level variables, it will be used. What about the layered model?