# What is a Responding Variable? - Definition & Example

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• 0:00 What is a Responding Variable?
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Lesson Transcript
Instructor
Megan Wahl

Megan has taught middle school science and developed curriculum for k-higher ed. She has a master's degree in Educational Technology.

Expert Contributor
Matthew Bergstresser

Matthew has a Master of Arts degree in Physics Education. He has taught high school chemistry and physics for 14 years.

In this lesson, you will learn what a responding variable is, and how it relates to the other variables in an experiment. You will also read an example of a simple experiment, and try to determine what the responding variable is.

## What is a Responding Variable?

The responding variable or dependent variable is a very important part of a scientific investigation. It is the part of the experiment that is observed for some kind of change or effect. To begin to understand the responding variable, we should first understand what a variable is. A variable is anything in an experiment that can change. Some examples of variables include: the temperature of a room, the amount of water given to a plant, the speed of a toy car or the concentration of salt in saltwater.

When scientists conduct investigations, they have to manage all of the variables involved in the study. They do this by taking care to plan out all aspects of the experiment, including the environment where the study will take place. For example, if you are measuring the effect of different wavelengths of light on the amount a plant grows, you would need to make sure the plants are not exposed to any other light sources by covering windows in the room.

Scientists begin by thinking of a possible relationship between two variables. For example, they may notice that certain objects are attracted to magnets while others are not. So they pose a scientific question, such as: which materials are attracted to magnets? Based on that question, they decide to change one variable on purpose, called the manipulated or independent variable and make a prediction, called the hypothesis, about what they think will happen.

Next, they plan to measure the response by watching another variable closely, called the responding or dependent variable. The responding variable is what is measured in an experiment. Sometimes a change will occur, and sometimes it will not, and other times something completely unexpected happens. Some experiments can have more than one responding variable, such as measuring both plant growth and then making other observations such as leaf color and the number of new leaves. In a controlled experiment, only one variable can be changed on purpose - the manipulated variable. All other variables must be kept the same. To make the experiment a fair test, only one thing can change on purpose, otherwise we won't know why the responding variable is changing.

## Examples

Let's look closely at an example:

A scientist wants to measure the effect of ground temperature on seed germination, so he forms a hypothesis: If the ground temperature is cooler than normal, seeds will take longer to germinate.

He decides to change the temperature of the soil seeds are placed in, the manipulated or independent variable, and plans to measure the number of days it takes for a seed to germinate. The responding variable is how many days it takes for the seeds to germinate. The responding variable tells the scientist whether or not the manipulated variable causes a change. It is very important that all other variables, such as the type of seed, type of soil, amount of water and light provided to the seeds, all stay the same. If all other variables are not held constant it is difficult to know why the responding variable changed.

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## Responding Variable

A responding variable is also known as a dependent variable. Multiple trials may be done when an experiment is conducted. In these trials a variable may be changed to test the outcome. For instance, if we are doing an experiment determining whether plants grow better in tap water or distilled water, the independent variables are the tap water and distilled water because we are changing them. The dependent variable or responding variable might be the height of the plants after being provided these two types of water. Let's practice determining the responding variables in some experiments.

### Directions

Determine what variable(s) are the responding variable in the practice problems.

### Practice Scenario

A student is determining which detergent removes mothball odor the best from clothes. The student bought a brand new pack of 6 white t-shirts. Each t-shirt is placed in a sealed container with 1 mothball for 2 days. After the 2 days, the shirts are removed from the sealed container, and each of them is placed in a sealed plastic bag. One t-shirt bag is labeled "control". These are the t-shirts we are going to compare the odor of the washed shirts to. The student then washes each t-shirt individually with three different detergents and compares the odor of the washed and dried shirts to the control shirts. The student ranks the odors on a 1-10 scale, with 10 being the control shirt odor.

The responding variable is the odor of the shirts after they are washed and dried. The odor of the shirts depends on the detergents.

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