Generally speaking, the rank variable belongs to a kind of classified variable, and the opposite is disorderly variable. The "satisfaction" that people often encounter in life is a hierarchical variable. Ordered classified variables refer to the differences in degree between the categories of their values, which gives people the feeling of "semi-quantitative", so they are also called hierarchical variables. Such as education (illiteracy, primary school, junior high school, high school, university, graduate student, etc.). ) and the evaluation results of students' moral operation (excellent, good, qualified and unqualified).

Educational measurement generally refers to an educational science that quantifies educational phenomena. This paper mainly studies the principles and methods of measuring the effect of education or training. In the popular sense, it only refers to the measurement of learning achievements-knowledge and skills. It originated from ancient examinations, but ancient examinations were not scientific educational measurements. At the beginning of the 20th century, American psychologist Thorndike and others applied the basic principles and methods of psychological statistics and measurement to education, which made educational measurement embark on a scientific road. Educational measurement plays an important role in talent selection, teaching students in accordance with their aptitude, educational evaluation and educational research.

The ratings of educational measurement are generally illiteracy, primary school, junior high school, high school, university, graduate student and so on. Or excellent, good, qualified, unqualified, so it belongs to one of the grade variables.