Use the Following Information for Questions

Short Answer

Use the following information for questions:
A researcher designed a study to assess whether grades in a statistics course could be improved by using a new teaching technique. The 250 students enrolled in a large introductory statistics class are also enrolled in one of 20 lab sections. The 20 lab sections are randomly divided into 2 groups of 10 lab sections each. The students in the first set of 10 lab sections are taught by this "new" method. The students in the remaining 10 lab sections are taught using the "old" techniques. The grades at the end of the term are then compared. Assume that the students do not know if the method they are being taught with is the old or the new method.
-Suppose the students in the "new" group were mostly upper-classmen and the students in the "old" group were mostly first and second-year students. What is the statistical name for the variable "year in school" in this study?