A rigorous economics paper generally needs three basic elements: viewpoint, frame of reference and analytical method. Viewpoint is the viewpoint to be demonstrated in this paper; The frame of reference provides some basic comparative measures for everyone to understand the economic reality.

A model is an abstraction of the real world. Because of the complexity of economic phenomenon itself, in actual analysis, it is necessary to strip off some variables that are irrelevant to the phenomenon concerned and abstract out key variables. According to some basic or obvious assumptions, the relationship between these variables is analyzed and some unexpected results are obtained.

Using econometric model for empirical analysis, its assumptions are more complicated and harsh. On the one hand, there are some assumptions in the economic theory referenced by empirical analysis; At the same time, there are some assumptions in the measurement model itself. Ignoring the former hypothesis usually leads to unexplained or biased empirical results.