Three Types of Variables

There are three types of variables you need to be concerned about when writing a thesis.  They are the independent, moderator, and dependent variables.

The Independent Variable

1.      The independent variable is not affected by the other variables. Its values are independent of changes in the values of other variables. It determines the values of other variables. The independent variable is manipulated by the researcher in that the researcher controls whether or not subjects are exposed to the independent variable.

An Example is teaching method.  It is not affected by any other variables, in fact it is the variable that does the affecting.

Treatments of the Independent Variable

The independent variable is controlled by the researcher, by splitting the subjects into different groups, with each group being associated with a different treatment (or value) of the independent variable.

For Example:  If you want to know if the achievement scores in a class will go up if there is a change in teaching method, you would divide the students into groups.  One group would be taught using a traditional method of teaching while the second group would be taught using a non traditional method of teaching.  The teaching method is the independent variable.

The Moderator Variable

2.   Moderator variables are characteristics that influence (moderate) the impact of the independent or treatment variable upon the dependent variable.

Moderator variables appear only in studies that include independent and dependent variables - usually experimental studies.

Baron and Kenny (1998) stated that:

In general terms, a moderator is a variable that affects the direction and/or strength of the relation between an independent or predictor variable and a dependent or criterion variable. Specifically within a correlational analysis framework, a moderator is a third variable that affects the zero-order correlation between two other variables. In the more familiar analysis of variance (ANOVA) terms, a basic moderator effect can be represented as an interaction between a focal independent variable and a factor that specifies the appropriate conditions for its operation. (p. 1174)

When you have divided the subjects into two groups, you can further divide them into age, sex, or class such as divergent learners, at-risk students, and social economic status. All of these factors are moderator variables.

The Dependent Variable

3.  The dependent variable is the variable affected by another variable the independent variable. The dependent variable is the variable that you believe might be influenced or modified by some treatment or exposure. It may also represent the variable you are trying to predict.

The dependent variable is measured to determine if the manipulation of the  independent variable had any effect. The new value of the dependent variable is caused by and depends on the value of the independent variable.

The dependent variable is sometimes called the outcome variable because it is measured and recorded by the researcher.  The dependent variable depends on what the subject will do.  The dependent variable is always what you are trying to explain; it is always the object of the research.

For example:

You want to see how a change in treatment (teaching method) will affect achievement scores of students.  The achievement scores are the dependent variable.

Group A                          Group B

Teaching Method   Teaching Method

Gender

Variables:

Independent variables:    Method of Teaching

Moderator Variable:    Gender

Levels:               Male vs. Female

Dependent Variable:   Student Achievement

The control will be the same teacher teaching the same students throughout the course.