A moderating variable is a factor that influences the strength or direction of the relationship between an independent and a dependent variable.
Here is a scholarly definition from Veronica Hefner (2017):
“The term moderating variable refers to a variable that can strengthen, diminish, negate, or otherwise alter the association between independent and dependent variables. Moderating variables can also change the direction of this relationship.”
Another way of looking at them is through a formula, which would look something like this:
“If x (independent variable) then y (dependent variable) will occur, but only under conditions z (moderating variable).” (Robbins, 2001, p. 445)
Robbins (2001, p. 445) provides a real-life example of how this equation works:
“To translate this into a real-life example, we might say that if we increase the amount of direct supervision in the work area (x), then there will be a change in worker productivity (y), but this effect will be moderated by the complexity of the tasks being performed (z).”
Examples of Moderating Variables
1. Age and Exercise Impact on Weight Loss
Primary Relationship: Exercise has a positive effect on weight loss.
Moderating Variable: Age
While exercise generally helps in weight loss, the age of an individual might modify how effective exercise is. For instance, younger individuals might lose weight more rapidly with a specific exercise regimen compared to older individuals. In this case, age acts as a moderating variable that influences the relationship between exercise and weight loss.
2. Advertising Exposure and Purchase Intent
Primary Relationship: Exposure to advertising increases the likelihood of intending to purchase a product.
Moderating Variable: Prior experience with the product
A person who has had a positive prior experience with a product might be more influenced by an advertisement for that product compared to someone who had a negative experience or no experience at all. The prior experience thus moderates the effect of advertising exposure on purchase intent.
3. Stress and Health Outcomes
Primary Relationship: High stress levels negatively affect health
Moderating Variable: Coping skills
Individuals with better coping skills or strategies might handle stress more effectively, reducing its detrimental impact on health. Those with poor coping skills might experience exacerbated health problems with similar levels of stress. Thus, coping skills moderate the relationship between stress and health outcomes.
4. Duration of Study and Exam Performance
Primary Relationship: Longer study durations are associated with better exam performance.
Moderating Variable: Quality of study material
If a student studies with high-quality, focused materials, they might perform better in exams with shorter durations of study compared to a student using outdated or less relevant study materials. Here, the quality of study material moderates the relationship between the duration of study and exam performance.
5. Social Media Use and Loneliness
Primary Relationship: Excessive social media use can increase feelings of loneliness.
Moderating Variable: Offline social support
Individuals with strong offline social support systems (like close friends or family) may not feel as lonely despite heavy social media use compared to those lacking such support. In this scenario, offline social support acts as a moderating variable between the relationship of social media use and feelings of loneliness.
6. Medication Dosage and Recovery from Illness
Primary Relationship: Higher doses of a medication lead to faster recovery.
Moderating Variable: Patient’s metabolism rate
Two patients taking the same medication dosage might have different recovery times if one metabolizes the drug faster than the other. A faster metabolism might lead to the drug being processed more efficiently, enhancing its effects, while a slower metabolism might mean the drug takes longer to show its impact. Here, the metabolism rate moderates the relationship between medication dosage and recovery speed.
7. Dietary Intake and Weight Gain
Primary Relationship: Consuming more calories results in weight gain.
Moderating Variable: Metabolic rate
Two individuals consuming the same number of calories might experience different rates of weight gain if one has a faster metabolic rate than the other. An individual with a faster metabolism might burn calories more quickly and gain less weight compared to someone with a slower metabolism. In this case, the metabolic rate moderates the relationship between dietary intake and weight gain.
8. Training and Job Performance
Primary Relationship: Undergoing training enhances job performance.
Moderating Variable: Prior knowledge on the subject
An employee with substantial prior knowledge about a training topic might derive less benefit from the training compared to an employee with limited prior knowledge. The person with prior knowledge might already be performing near their peak, so the training has a diminished effect. Hence, prior knowledge acts as a moderating variable between training and its impact on job performance.
9. Sun Exposure and Skin Damage
Primary Relationship: More sun exposure leads to increased skin damage.
Moderating Variable: Use of sunscreen
An individual who uses sunscreen regularly might experience less skin damage from the sun compared to someone who doesn’t, even if both spend the same amount of time in the sun. The sunscreen moderates the effect of sun exposure on skin damage by providing a protective layer.
10. Physical Activity and Cardiovascular Health
Primary Relationship: Regular physical activity improves cardiovascular health.
Moderating Variable: Genetic predisposition to heart conditions
While physical activity generally benefits cardiovascular health, an individual with a strong genetic predisposition to heart conditions might not see the same degree of improvement as someone without this predisposition. The genetic factor thus moderates the relationship between physical activity and cardiovascular health outcomes.
11. Class Attendance and Academic Achievement
Primary Relationship: Regular class attendance leads to higher academic achievement.
Moderating Variable: Quality of classroom instruction
A student attending classes with a highly effective and engaging instructor might experience a more significant boost in academic achievement compared to a student attending classes with a less competent instructor. In this case, the quality of classroom instruction moderates the relationship between class attendance and academic success.
12. Therapy Sessions and Mental Well-being
Primary Relationship: Attending therapy sessions can improve mental well-being.
Moderating Variable: Client-therapist rapport
client who has a strong, trusting relationship with their therapist might derive more benefit from therapy sessions compared to a client who doesn’t connect as well with their therapist. The strength of the client-therapist rapport acts as a moderating variable between attending therapy sessions and improvements in mental well-being.
13. Caffeine Intake and Alertness
Primary Relationship: Consuming caffeine increases alertness.
Moderating Variable: Tolerance to caffeine
An individual who consumes caffeine regularly and has built a tolerance might not experience the same boost in alertness from a single cup of coffee as someone who rarely consumes caffeine. Tolerance to caffeine moderates the relationship between caffeine intake and its effect on alertness.
14. Savings and Financial Security
Primary Relationship: Regular savings contribute to financial security.
Moderating Variable: Economic environment
An individual who saves money regularly might not achieve the same level of financial security during an economic recession as they would during a booming economy. The economic environment acts as a moderating variable between the act of saving and the level of financial security achieved.
15. Watering Plants and Plant Growth
Primary Relationship: Regular watering promotes plant growth.
Moderating Variable: Quality of soil
A plant in fertile, nutrient-rich soil might grow more robustly with regular watering compared to a plant in poor, nutrient-deficient soil. Even if both plants receive the same amount of water, the quality of soil moderates the relationship between watering and plant growth.
Moderating vs Confounding Variables
Moderating variables and confounding variables are similar in that they affect the relationship between the independent and dependent variables. However, in general, confounding variables introduce bias that can distort the perceived relationship, whereas moderating variables simply specify conditions under which the relationship changes in strength or direction (Nestor & Schutt, 2018).
A moderating variable affects the direction and/or strength of the relation between an independent and a dependent variable. The presence of a moderating variable implies that the relationship between two other variables changes depending on the level or presence of the moderator.
On the other hand, a confounding variable, also known as a confounder or lurking variable, is an extraneous variable in a statistical model that correlates (positively or negatively) with both the dependent variable and the independent variable.
The presence of a confounding variable can give a false impression of a relationship between the independent and dependent variables. If not controlled for, confounders can distort or confound the real effect of the independent variable on the dependent variable (Boniface, 2019).
So, while both moderating and confounding variables influence the relationships between primary variables, they do so in different ways. Moderators affect the strength or direction of the relationship, while confounders introduce bias by giving a false impression of a relationship where one may not exist or masking a relationship that does (Stapel & van Beek, 2015).
Moderating vs Mediating Variables
A moderating variable affects the strength or direction of the relationship between the independent and dependent variables, whereas a mediating variable explains the process or mechanism through which the independent variable affects the dependent variable (Hefner, 2017).
The mediating variable intervenes between the independent and dependent variables, clarifying how or why they are connected (Stapel & van Beek, 2015).
For example, a mediating variable might explain how stress (independent variable) leads to poor health outcomes (dependent variable) by showing that increased stress levels result in reduced sleep quality (mediating variable), which in turn impacts health.
In essence, while moderating variables describe “when” or “for whom” a relationship holds, mediating variables explain “how” or “why” a relationship occurs (Stapel & van Beek, 2015).
Boniface, D. R. (2019). Experiment Design and Statistical Methods For Behavioural and Social Research. CRC Press. ISBN: 9781351449298.
Hefner, V. (2017). Variables, Moderating Types. In Allen, M. (Ed.) The SAGE Encyclopedia of Communication Research Methods. SAGE Publications.
Nestor, P. G., & Schutt, R. K. (2018). Research Methods in Psychology: Investigating Human Behavior. SAGE Publications.
Stapel, B. & van Beek, R.J. (2015). Confounders, moderators and mediators. In Mellenbergh, G. J., & Adèr, H. J. (Eds.). Advising on Research Methods: Selected Topics 2014. Johannes van Kessel Advising.
Dr. Chris Drew is the founder of the Helpful Professor. He holds a PhD in education and has published over 20 articles in scholarly journals. He is the former editor of the Journal of Learning Development in Higher Education. [Image Descriptor: Photo of Chris]