Mediator vs moderator—which is right for you?

There has always been some confusion between mediators and moderators when conducting research. It’s understandable. The two words even look and sound similar. But when dealing with statistical variables, they’re very different, and determining which is the right one for you can be complex.  

Including mediators and moderators in your research not only allows you to study the relationship between two variables but can also help you avoid biases that could occur without them. Read further to learn more about how to distinguish and apply mediators and moderators in research.  

Mediators provide a way for independent variables (aka causal variables or intervention) to impact a dependent variable (aka an outcome or effect). They explain the how and why relationship between the two. A mediator is always caused by the independent variable and influences the dependent variable. Consider a mediator as the “middleman” between independent and dependent variables. 

When using mediators, you can learn how or why an effect takes place. When using mediation analysis, you’re testing a hypothetical causal chain. If variable A affects variable B, then it turns into variable C.   

Perhaps an easier way to understand it is mediation analysis gives us information about how or why the independent variable affects the dependent variable. Taking the mediator out of the model in complete mediation eliminates the relationship between the dependent and independent variables. This is because the mediator thoroughly explains the relationship between the dependent and independent variables, and without it, there’s no relationship.

You can use a mediator in your research to see if the influence of the mediator is stronger than the direct influence of the independent variable. A mediator carries an effect to the direct variable from the indirect variable. 

A mediation flow chart might read: the independent variable causes the mediator, the mediator must change the dependent variable, and the mediator changes the relationship or correlation between the independent and the dependent variables.   

While mediation answers the how and why, moderators look at interactions. Moderation analysis is the level that the relationship between the independent and dependent variables changes as a function of a third variable or the moderator. 

Moderator variables are sometimes referred to as interactions or products because they can affect the strength or direction of the relationship between the independent and dependent variables. They make the relationship stronger or weaker or change it from strong to moderate to no influence at all.

Moderators can be either quantitative or qualitative. Examples of quantitative moderators might be numerical values such as test scores, weight, age, IQ, etc. Examples of qualitative moderators would be factors with no numeric value, such as gender, race, or education. 

The moderator can also be changed to determine the amount of change in the relationship between the variables since it influences the level, direction, or strength of the relationship.  

The purpose of using a moderator in your research is to help you determine what categorical or quantitative variables change the relationship between your independent and dependent variables or to determine if there’s any validity to the moderator you have chosen and the changes predicted.

Partial or complete mediation

We can talk about partial or complete mediation. 

In complete or full mediation, a mediator explains the relationship between the independent and dependent variables. If the mediator is removed, a relationship no longer exists, explaining why it’s called complete.  

With partial mediation, when the mediator is removed from the model, there’s still a statistical relationship between the independent and dependent variables, meaning the mediator only partially explains the relationship.

Strength and direction of the effect

Moderation in research refers to the extent to which the relationship between two variables changes depending on the level of a third variable, which is known as the moderator variable. A moderator can change the strength and direction of the relationship between the independent and dependent variables.  

Mediation analysis

Mediation analysis uses either an analysis of variance or linear regression analysis to test whether a variable is a mediator. As explained previously, mediation may either be partial or complete. Mediators are caused by the independent variable, and they also influence the dependent variable. 

Moderation analysis

Moderation analysis is a commonly used technique in statistical modeling to help understand the nature of the relationships between variables and to identify the conditions under which those relationships are strongest or weakest. Moderation analysis can be conducted using various statistical methods, such as multiple regression, ANOVA, and structural equation modeling. 

Moderators used in research can be categorical, such as race, gender, religion, etc., and are usually not quantifiable, or they can be quantitative, such as age, income, weight, etc. If a moderator is removed, a relationship will still exist between the independent and dependent variables—unlike when a mediator is removed from complete mediation.  

A simple example of a mediator variable:

Exercise affects family relationships because it creates endorphins.

Exercise is the independent variable, and family relationships are the dependent variable.  Endorphins are the mediator.

Without the mediator, your variables don’t have a relationship with each other.  However, when looking at moderators, as in the next example, there would still be a relationship, but a moderator explains how the variables are affected.

A simple example of a moderator example:

Seniors are more likely to have accidents due to vision impairments.

Accidents are the independent variable, vision impairments are the dependent variable, and seniors are the moderator (age being the variable you use to create the group 'seniors').

A mediator is the mechanism of a relationship between two variables: it explains the process by which they’re related. A confounder, however, is a third variable that affects variables of interest and makes them appear related when they actually are not.

IVs (independent variables) and DVs (dependent variables) are different from a mediator. The mediator variable is used to explain the relationship between the independent variable and the dependent variable. Without the mediator variable, there’s no relationship between the other two in the case of complete mediation.

When mediation is in place, there’s a correlation between the independent variable and the mediator variable, as well as a correlation between the mediator variable and the dependent variable. 

In other words, mediation occurs when the relationship between the independent variable and the dependent variable is partially or completely explained by the mediator variable, which in turn means that there is a correlation between the independent variable and the mediator variable and between the mediator variable and the dependent variable.  

Put simply, it’s seen as a mediator variable if the change in the level of the independent variable significantly accounts for the variation in the other variable. 

If work experience influences starting salary, how big a role does gender play? Work experience is the independent variable, salary is the dependent variable, and gender is the moderator. 

Yes, a variable can be both moderating and mediating, although the two roles are distinct and serve different purposes in statistical analysis. It’s dependent on the framing of the study and the independent variable and dependent variable you’re working with. 

Consider that a variable can be both a mediator and a moderator when it affects both the strength and the direction of the relationship between two variables and also explains the mechanism through which the relationship occurs. 

A confounder is a variable that’s related to both the predictor of interest and the outcome, but it’s not on the causal pathway. A moderator is a variable that changes the direction or strength of the relationship between the independent and the dependent variables.

To identify a moderating variable in research, you must look for a variable that influences the direction or strength of the relationship between the independent and dependent variables. Overall, identifying a moderating variable requires careful consideration of the research question, theoretical framework, and data analysis techniques used in the study. 

A mediator relationship is a type of relationship in which a third variable, called a mediator, explains the relationship between two other variables. More specifically, a mediator variable that acts as a “middleman” explains how or why two other variables are related to each other. 

A moderator relationship, also known as an interaction or conditioning effect, is one where the independent and dependent variables have a relationship, but by adding the third, or a moderating variable, the relationship changes. Moderators point out the when, who, or under what circumstances.

No, a mediator variable and a moderator variable are two distinct concepts in statistical analysis and cannot be the same variable.

A mediator variable explains the relationship between two other variables. A moderator variable affects the direction or strength of the relationship between two other variables.