When reading articles about new studies, you may see the terms independent and dependent variables used. If you’re not in a field that uses these terms frequently, they may cause some confusion. An independent variable describes a variable whose changes are not affected by any other variable in the study. The dependent variable is the opposite. It is the subject matter being studied, and the other variables in the study cause its changes.

01## Plant Type vs. Height

Let’s say that you’re interested in buying some plants and you want to see what type of plant grows the fastest if you give each of them equal amounts of water. In this example, it’s fairly easy to define the independent and dependent variables. First, list the variables in this experiment and then identify those which are independent and those that are dependent. The variables are the type of plant and the height of each plant. Because the amount of water isn’t changing, it isn’t either option.

Now, to determine which of the variables is independent, we must think about which variable is affected by the other variable. The type of plant isn’t affected by the height of each plant, so the plant’s type is the independent variable. This makes the height of the plants the dependent variable because the height does depend on the type of plant.

02## Drink Preference vs. Flavor

In a test where a single person tries several beverages and determines which drink they prefer, it is very easy to determine the independent and dependent variables. The variables in this situation are the flavor of drink and the tester’s level of preference. The tester himself never changes, so he is not an independent or dependent variable.

The independent variable is the flavor of each drink. This isn’t being studied, and it isn’t affected by his preference level. The dependent variable is his preference level because it is being measured and does rely on the flavor.

03## Sleep vs. Test Scores

A school wants to discover whether or not the amount of sleep a student gets affects their test scores. The variables in this problem are the amount of sleep and the test scores. The test scores depend on the amount of sleep, so they are the dependent variable while the amount of sleep is the independent variable.

04## Caffeine vs. Tiredness

If you wanted to find out how tired you felt after certain amounts of caffeine, it would be fairly simple to determine which are the independent and dependent variables. Your tiredness would depend on how much caffeine you had, making your tiredness the dependent variable. The amount of caffeine is the independent variable.

05## Wages vs. Task vs. Quality of Work

Getting a bit more complex, think about a job that offers a variety of tasks. The amount you are paid is based on the quality of your work, but each task has a different starting wage. If you wanted to find out how much money you would earn, it would help to know the dependent and independent variables. The variables are the type of task, the starting wage, and the quality of work.

- Quality of work doesn’t depend on any of the other listed variables. It is an independent variable.
- The total amount of money earned depends on the task and the quality of work. It is a dependent variable.
- The type of task doesn’t depend on any of the other variables, so it is an independent variable.
- The starting wage depends on the type of task. It is a dependent variable.

06## Response Times vs. Sound

Researchers are interested in discovering the amount of time people take to respond to specific noises. In an example like this, the variables are the length of time it takes each person to respond and the type of noise they are responding to. However, depending on how detailed the study is, there could be even more variables that are not explicitly stated. For example, the people in the group may not be the same age or sex. They may have different jobs. Determining the independent and dependent variables can become significantly more difficult as the number of variables increase.

The dependent variable is the time it takes for each person to respond. Every other variable listed is independent because they do not change as a result of any of the other variables.

07## Moths vs. Brightness

If a scientist wanted to discover whether or not moths were attracted to a certain level of brightness in lights, she could list out several variables. The first variable is the level of brightness. Then, maybe she wants to try it out on different species of moth. That’s another variable. Finally, we have the level of attraction. The only dependent variable is the level of attraction. The other variables aren’t being measured and aren’t changed by the other variables.

08## Dissolved Sugar vs. Temperature

A person might wonder if heating water will help sugar dissolve faster. The variables in this problem are the temperature of the water, the amount of sugar that dissolves completely, type of sugar, and method of stirring. In an experiment like this, you would want to keep the stirring variable and type of sugar variable consistent. They are neither independent or dependent. The amount of dissolved sugar is what you would be measuring, and because it is the variable affected by the water temperature, it is considered the dependent variable.

09## Cost of Living

To find an individual’s cost of living, you would need to consider variables such as salary, age, location, marital status, and expenses. Each of the listed variables is independent while the actual cost of living is dependent. The cost of living is what is being measured, and it is heavily affected by the other variables.

10## Real Life Variables

Picking out the independent and dependent variables can be done outside of singular studies and tests. This can be even more difficult than before because, in real life, there is no end to the number of variables. For example, the number of sales depends on variables such as customer demographics, weather, and store location. These are all independent variables. However, you could continue adding to that list with a million other potential variables, so it is important to remember the basic rules. If it is being measured and is affected by other variables, it is a dependent variable.