An independent variable (IV) is what is manipulated in a scientific experiment to determine its effect on the dependent variable (DV).
By varying the level of the independent variable and observing associated changes in the dependent variable, a researcher can conclude whether the independent variable affects the dependent variable or not.
This can provide very valuable information when studying just about any subject.
Because the researcher controls the level of the independent variable, it can be determined if the independent variable has a causal effect on the dependent variable.
The term causation is vitally important. Scientists want to know what causes changes in the dependent variable. The only way to do that is to manipulate the independent variable and observe any changes in the dependent variable.
Definition of Independent and Dependent Variables
The independent variable and dependent variable are used in a very specific type of scientific study called the experiment.
Although there are many variations of the experiment, generally speaking, it involves either the presence or absence of the independent variable and the observation of what happens to the dependent variable.
The research participants are randomly assigned to either receive the independent variable (called the treatment condition), or not receive the independent variable (called the control condition).
Other variations of an experiment might include having multiple levels of the independent variable.
If the independent variable affects the dependent variable, then it should be possible to observe changes in the dependent variable based on the presence or absence of the independent variable.
Of course, there are a lot of issues to consider when conducting an experiment, but these are the basic principles.
These concepts should not be confused with predictor and outcome variables.
Examples of Independent and Dependent Variables
1. Gatorade and Improved Athletic Performance
A sports medicine researcher has been hired by Gatorade to test the effects of its sports drink on athletic performance. The company wants to claim that when an athlete drinks Gatorade, their performance will improve.
If they can back up that claim with hard scientific data, that would be great for sales.
So, the researcher goes to a nearby university and randomly selects both male and female athletes from several sports: track and field, volleyball, basketball, and football. Each athlete will run on a treadmill for one hour while their heart rate is tracked.
All of the athletes are given the exact same amount of liquid to consume 30-minutes before and during their run. Half are given Gatorade, and the other half are given water, but no one knows what they are given because both liquids have been colored.
In this example, the independent variable is Gatorade, and the dependent variable is heart rate.
2. Chemotherapy and Cancer
A hospital is investigating the effectiveness of a new type of chemotherapy on cancer. The researchers identified 120 patients with relatively similar types of cancerous tumors in both size and stage of progression.
The patients are randomly assigned to one of three groups: one group receives no chemotherapy, one group receives a low dose of chemotherapy, and one group receives a high dose of chemotherapy.
Each group receives chemotherapy treatment three times a week for two months, except for the no-treatment group. At the end of two months, the doctors measure the size of each patient’s tumor.
In this study, despite the ethical issues (remember this is just a hypothetical example), the independent variable is chemotherapy, and the dependent variable is tumor size.
3. Interior Design Color and Eating Rate
A well-known fast-food corporation wants to know if the color of the interior of their restaurants will affect how fast people eat. Of course, they would prefer that consumers enter and exit quickly to increase sales volume and profit.
So, they rent space in a large shopping mall and create three different simulated restaurant interiors of different colors. One room is painted mostly white with red trim and seats; one room is painted mostly white with blue trim and seats; and one room is painted mostly white with off-white trim and seats.
Next, they randomly select shoppers on Saturdays and Sundays to eat for free in one of the three rooms. Each shopper is given a box of the same food and drink items and sent to one of the rooms. The researchers record how much time elapses from the moment they enter the room to the moment they leave.
The independent variable is the color of the room, and the dependent variable is the amount of time spent in the room eating.
4. Hair Color and Attraction
A large multinational cosmetics company wants to know if the color of a woman’s hair affects the level of perceived attractiveness in males. So, they use Photoshop to manipulate the same image of a female by altering the color of her hair: blonde, brunette, red, and brown.
Next, they randomly select university males to enter their testing facilities. Each participant sits in front of a computer screen and responds to questions on a survey. At the end of the survey, the screen shows one of the photos of the female.
At the same time, software on the computer that utilizes the computer’s camera is measuring each male’s pupil dilation. The researchers believe that larger dilation indicates greater perceived attractiveness.
The independent variable is hair color, and the dependent variable is pupil dilation.
5. Mozart and Math
After many claims that listening to Mozart will make you smarter, a group of education specialists decides to put it to the test. So, first, they go to a nearby school in a middle-class neighborhood.
During the first three months of the academic year, they randomly select some 5th-grade classrooms to listen to Mozart during their lessons and exams. Other 5th grade classrooms will not listen to any music during their lessons and exams.
The researchers then compare the scores of the exams between the two groups of classrooms.
Although there are a lot of obvious limitations to this hypothetical, it is the first step.
The independent variable is Mozart, and the dependent variable is exam scores.
6. Essential Oils and Sleep
A company that specializes in essential oils wants to examine the effects of lavender on sleep quality. They hire a sleep research lab to conduct the study. The researchers at the lab have their usual test volunteers sleep in individual rooms every night for one week.
The conditions of each room are all exactly the same, except that half of the rooms have lavender released into the rooms and half do not. While the study participants are sleeping, their heart rates and amount of time spent in deep sleep are recorded with high-tech equipment.
At the end of the study, the researchers compare the total amount of time spent in deep sleep of the lavender-room participants with the no lavender-room participants.
The independent variable in this sleep study is lavender, and the dependent variable is the total amount of time spent in deep sleep.
7. Teaching Style and Learning
A group of teachers is interested in which teaching method will work best for developing critical thinking skills.
So, they train a group of teachers in three different teaching styles: teacher-centered, where the teacher tells the students all about critical thinking; student-centered, where the students practice critical thinking and receive teacher feedback; and AI-assisted teaching, where the teacher uses a special software program to teach critical thinking.
At the end of three months, all the students take the same test that assesses critical thinking skills. The teachers then compare the scores of each of the three groups of students.
The independent variable is the teaching method, and the dependent variable is performance on the critical thinking test.
8. Concrete Mix and Bridge Strength
A chemicals company has developed three different versions of their concrete mix. Each version contains a different blend of specially developed chemicals. The company wants to know which version is the strongest.
So, they create three bridge molds that are identical in every way. They fill each mold with one of the different concrete mixtures. Next, they test the strength of each bridge by placing progressively more weight on its center until the bridge collapses.
In this study, the independent variable is the concrete mixture, and the dependent variable is the amount of weight at collapse.
9. Recipe and Consumer Preferences
People in the pizza business know that the crust is key. Many companies, large and small, will keep their recipe a top secret. Before rolling out a new type of crust, the company decides to conduct some research on consumer preferences.
The company has prepared three versions of their crust that vary in crunchiness, they are: a little crunchy, very crunchy, and super crunchy. They already have a pool of consumers that fit their customer profile and they often use them for testing.
Each participant sits in a booth and takes a bite of one version of the crust. They then indicate how much they liked it by pressing one of 5 buttons: didn’t like at all, liked, somewhat liked, liked very much, loved it.
The independent variable is the level of crust crunchiness, and the dependent variable is how much it was liked.
10. Protein Supplements and Muscle Mass
A large food company is considering entering the health and nutrition sector. Their R&D food scientists have developed a protein supplement that is designed to help build muscle mass for people that work out regularly.
The company approaches several gyms near its headquarters. They enlist the cooperation of over 120 gym rats that work out 5 days a week. Their muscle mass is measured, and only those with a lower level are selected for the study, leaving a total of 80 study participants.
They randomly assign half of the participants to take the recommended dosage of their supplement every day for three months after each workout. The other half takes the same amount of something that looks the same but actually does nothing to the body.
At the end of three months, the muscle mass of all participants is measured.
The independent variable is the supplement, and the dependent variable is muscle mass.
11. Air Bags and Skull Fractures
In the early days of airbags, automobile companies conducted a great deal of testing. At first, many people in the industry didn’t think airbags would be effective at all. Fortunately, there was a way to test this theory objectively.
In a representative example: Several crash cars were outfitted with an airbag, and an equal number were not. All crash cars were of the same make, year, and model. Then the crash experts rammed each car into a crash wall at the same speed. Sensors on the crash dummy skulls allowed for a scientific analysis of how much damage a human skull would incur.
The amount of skull damage of dummies in cars with airbags was then compared with those without airbags.
The independent variable was the airbag and the dependent variable was the amount of skull damage.
12. Vitamins and Health
Some people take vitamins every day. A group of health scientists decides to conduct a study to determine if taking vitamins improves health.
They randomly select 1,000 people that are relatively similar in terms of their physical health. The key word here is “similar.”
Because the scientists have an unlimited budget (and because this is a hypothetical example, all of the participants have the same meals delivered to their homes (breakfast, lunch, and dinner), every day for one year.
In addition, the scientists randomly assign half of the participants to take a set of vitamins, supplied by the researchers every day for 1 year. The other half do not take the vitamins.
At the end of one year, the health of all participants is assessed, using blood pressure and cholesterol level as the key measurements.
In this highly unrealistic study, the independent variable is vitamins, and the dependent variable is health, as measured by blood pressure and cholesterol levels.
13. Meditation and Stress
Does practicing meditation reduce stress? If you have ever wondered if this is true or not, then you are in luck because there is a way to know one way or the other.
All we have to do is find 90 people that are similar in age, stress levels, diet and exercise, and as many other factors as we can think of.
Next, we randomly assign each person to either practice meditation every day, three days a week, or not at all. After three months, we measure the stress levels of each person and compare the groups.
How should we measure stress? Well, there are a lot of ways. We could measure blood pressure, or the amount of the stress hormone cortisol in their blood, or by using a paper and pencil measure such as a questionnaire that asks them how much stress they feel.
In this study, the independent variable is meditation and the dependent variable is the amount of stress (however it is measured).
14. Video Games and Aggression
When video games started to become increasingly graphic, it was a huge concern in many countries in the world. Educators, social scientists, and parents were shocked at how graphic games were becoming.
Since then, there have been hundreds of studies conducted by psychologists and other researchers. A lot of those studies used an experimental design that involved males of various ages randomly assigned to play a graphic or non-graphic video game.
Afterward, their level of aggression was measured via a wide range of methods, including direct observations of their behavior, their actions when given the opportunity to be aggressive, or a variety of other measures.
So many studies have used so many different ways of measuring aggression.
In these experimental studies, the independent variable was graphic video games, and the dependent variable was observed level of aggression.
15. Vehicle Exhaust and Cognitive Performance
Car pollution is a concern for a lot of reasons. In addition to being bad for the environment, car exhaust may cause damage to the brain and impair cognitive performance.
One way to examine this possibility would be to conduct an animal study. The research would look something like this: laboratory rats would be raised in three different rooms that varied in the degree of car exhaust circulating in the room: no exhaust, little exhaust, or a lot of exhaust.
After a certain period of time, perhaps several months, the effects on cognitive performance could be measured.
One common way of assessing cognitive performance in laboratory rats is by measuring the amount of time it takes to run a maze successfully. It would also be possible to examine the physical effects of car exhaust on the brain by conducting an autopsy.
In this animal study, the independent variable would be car exhaust and the dependent variable would be amount of time to run a maze.
Read Next: Extraneous Variables Examples
The experiment is an incredibly valuable way to answer scientific questions regarding the cause and effect of certain variables. By manipulating the level of an independent variable and observing corresponding changes in a dependent variable, scientists can gain an understanding of many phenomena.
For example, scientists can learn if graphic video games make people more aggressive, if mediation reduces stress, if Gatorade improves athletic performance, and even if certain medical treatments can cure cancer.
The determination of causality is the key benefit of manipulating the independent variable and them observing changes in the dependent variable. Other research methodologies can reveal factors that are related to the dependent variable or associated with the dependent variable, but only when the independent variable is controlled by the researcher can causality be determined.
Ferguson, C. J. (2010). Blazing Angels or Resident Evil? Can graphic video games be a force for good? Review of General Psychology, 14(2), 68-81. https://doi.org/10.1037/a0018941
Flannelly, L. T., Flannelly, K. J., & Jankowski, K. R. (2014). Independent, dependent, and other variables in healthcare and chaplaincy research. Journal of Health Care Chaplaincy, 20(4), 161–170. https://doi.org/10.1080/08854726.2014.959374
Manocha, R., Black, D., Sarris, J., & Stough, C.(2011). A randomized, controlled trial of meditation for work stress, anxiety and depressed mood in full-time workers. Evidence-Based Complementary and Alternative Medicine, vol. 2011, Article ID 960583. https://doi.org/10.1155/2011/960583
Rumrill, P. D., Jr. (2004). Non-manipulation quantitative designs. Work (Reading, Mass.), 22(3), 255–260.
Taylor, J. M., & Rowe, B. J. (2012). The “Mozart Effect” and the mathematical connection, Journal of College Reading and Learning, 42(2), 51-66. https://doi.org/10.1080/10790195.2012.10850354