According to the depth of research, it can be divided into descriptive topics, causal topics and predictive topics.

(1) Descriptive topic refers to a detailed description of the real situation of social phenomena, which is the most basic topic with low difficulty and low level.

(2) Causality question refers to revealing the causal relationship between two or more social phenomena, and mainly answers "why" and "how to do it", which is of high level and difficult.

(3) Predictive topic refers to predicting the future development trend and situation of things on the basis of clarifying the causal relationship of social phenomena. The research level is the highest, which is of great significance to practical work and theoretical research.