What Are Variables? How To Choose Variables For Your Science Project

Scientists want to know how things work. They want to understand why things happen and use that information to predict what will happen in the future. To do this, they use experiments to see if one thing causes another thing to happen. They follow a special process called the scientific method to design their experiments.

In an experiment, all of the things that can change are called variables. There are three types of variables in a good experiment: independent variables, dependent variables, and controlled variables.

What is an independent variable?

The independent variable is the one thing that the scientist changes. Scientists change only one thing at a time in an experiment because it helps them figure out what is causing the results they see. If they changed more than one thing, it would be hard to know which change was making a difference. For example, if a scientist wanted to know how the size of a dog affects how much food it eats, they would only change the size of the dogs in the experiment. They would not change other variables like the time of day the dogs are fed, or the type of food they are offered. If scientists changed more than one thing, they would not know whether a dog ate more because it was bigger or because it was extra hungry from being fed later in the day.

Sometimes, scientists have to change more than one thing, and that can be tricky. They use special math, called statistics, and more experiments to understand how much each variable changed the results. But for a science fair project, it's usually best to focus on just one thing at a time. If you're new to doing science projects and want to explore how more than one variable affects something, you can do multiple experiments where you change one independent variable at a time.

What is a dependent variable?

The dependent variables are the things in an experiment that the scientist observes and measures. Scientists want to know if changing the independent variable has an effect on the dependent variables. In our dog example, the dependent variable is how much the dogs eat. This is what we are watching and measuring. It's called the "dependent" variable because we want to see if it depends on the independent variable. If there is a connection between the two variables, it might mean that one thing causes the other. There can be more than one dependent variable in an experiment.

What is a controlled variable?

Controlled variables are all of the things that scientists want to make sure to keep the same during an experiment. They are important because they help us understand the effect of the one thing we are testing.

Let's go back to our dog example. To understand whether being larger or smaller causes a dog to eat more or less food we need to control all the other variables. We need to make sure things like how hungry the dogs are at the start, the type of food we give them, and if they like the food or not are not changing. If we don't control these things, we might get different results for reasons other than the dogs' size. Maybe one dog is just really hungry that day, or maybe another dog doesn't like the food we gave him. We keep all these other things the same so we can see the real effect of a dog's size on how much it eats.

What makes a good variable?

A good variable is one that can be measured. For example, we can easily measure the weight or temperature of something. But imagine if we wanted to do an experiment about love. Love is not something we can measure with a tool. It's more of a feeling, and different people might have different opinions about it. So, love would not be a good variable to use in a science project.