A criterion variable is nothing but the dependent variable. As the name suggests the value of the dependent/criterion variable depends on the value of the independent/predictor variable.
The predictor variables are the independent variables and the criterion variables are the dependent variables. Let us try to understand this by looking at some examples.
Example 1: Time Spent Studying vs Marks in Exam
Criterion variable is a term used for dependent variables in the context of linear regression. Suppose you construct a statistical model to study the relationship between the number of hours spent studying and marks obtained in an exam.
Since the marks obtained depend on the number of hours spent studying, the marks obtained are the dependent/criterion variable. The number of hours spent studying is the predictor (independent) variable since we can use it to predict the marks obtained.
Predictor Variable: Hours Spent Studying.
Criterion Variable: Marks Obtained in the Exam.
Note that in the above example, there is an actual causal relationship between the two variables. This need not be the case every time we see a correlation between two variables.
Example 2: Height vs Shoe Size
Consider the relationship between the height of a person and the shoe size of the person. There is definitely a relationship between these two variables. Generally speaking, as a person grows up his shoe size increases and his height also increases.
We can construct a linear regression model between these two variables taking the predictor variable to be the shoe size of the person and the criterion variable to be the height of the person. We can obtain predictions for the height by inputting the shoe size in our regression.
Predictor Variable: Shoe Size.
Criterion/Dependent Variable: Height.
Notice then in this example, we cannot infer a causal relationship between the two variables. Indeed it would be absurd to claim that the increase in shoe size caused a corresponding increase in the height of the person.
Criterion Variable in Psychology:
The criterion variable in psychology is the dependent variable in our study. As an example consider the relationship between the attendance rate and the grade point average of students in a particular class.
It is an empirical observation that a higher attendance rate is correlated with a higher GPA. In this situation, the attendance rate is the predictor variable. Since the grade point average depends on the attendance rate, the GPA is the criterion/dependent variable.
Predictor Variable: Attendance Rate.
Criterion/Dependent Variable: GPA.
Predictor Variable vs Criterion Variable:
The main difference between the predictor and criterion variable is that the predictor variable is another name for the independent variable whereas the criterion variable is the dependent variable.
By manipulating the predictor variable, we can cause a change in the value of the criterion variable. This establishes that there is a correlation between the two variables.
Consider an example from agricultural studies. Suppose that we want to understand the relationship between crop yield and the amount of fertilizer used. In this situation, the amount of fertilizer is the predictor variable and the crop yield is the criterion variable.
The crop yield depends on the amount of fertilizer used and it is reasonable to expect that a greater use of fertilizer would lead to a higher crop yield.