Conceptual framework: Moderating variables

When creating a conceptual framework to explore a cause-and-effect relationship, you often need to deal with moderating variables, also known as moderators.

Moderating variables in a conceptual framework

This is a continuation of an article that explained how to create a conceptual framework. Our example framework maps the relationship between “hours of study” (independent variable) and “exam score” (dependent variable).

Now we’ll expand the framework by adding a moderating variable. A moderator alters the effect that an independent variable has on a dependent variable, on the basis of the moderator’s value.

The moderator thus changes the effect component of the cause-and-effect relationship. This moderation is also referred to as the interaction effect.

Conceptual framework with a moderator variable

In this example, we expect that the number of hours a student studies is related to their exam score: the more you prepare, the higher your score will be.

Now we add the moderator “IQ.” A student’s IQ level changes the effect that the variable “hours of study” has on the exam score: the higher your IQ, the fewer hours of study you must put in to do well on the exam.

In other words, the “IQ” moderator moderates the effect that the number of study hours has on the exam score.

This effect is illustrated in Figure 1. In this graphic, it’s easy to see how the number of hours spent studying affects the exam score. The more hours you study, the better your results. A student who studies for 20 hours will get a perfect score.

Figure 1: Effect hours of study on exam score

An “IQ” moderator of 120 has been added in Figure 2 below. A student with this IQ will already achieve a perfect score after just 15 hours of study.

Figure 2: Effect of hours of study on exam score with an IQ moderator of 120

In Figure 3, the value of the “IQ” moderator has been increased to 150. A student with this IQ will only need to invest five hours of studying in order to get a perfect score.

Figure 3: Effect of hours of study on exam score with an IQ moderator of 150

The higher the IQ, the fewer hours a student needs to study in order to achieve a score of 100%.

In short, a moderating variable is something that changes the cause-and-effect relationship between two variables as its value increases or decreases.

Moderator vs mediator

It’s important not to confuse a moderator with a mediator. A mediating variable does not only affect the outcome of the dependent variable – it is also affected by the independent variable. Therefore, it helps explain the relationship between the independent and dependent variable.

For example, the variable “number of practice problems completed” is a mediator: the more hours you study, the more problems you will complete; the more practice problems you complete, the higher your score will be.  A mediator links the independent and dependent variables.

However, no matter how many hours you study, your IQ will not get higher. A moderator is not impacted by the independent variable.