There are three main types of experiment variables that our students must be aware of, especially when approaching the science fair project. They are the independent variable, the dependent variable, and the controlled variable. 

In today’s science corner, we are going to look closer at each of these variables. 

The Three Main Types of Experiments

Independent Variables

The independent experiment variable is the factor that is controlled or changed by the scientist performing the experiment. 

Ask your students the following question to determine the independent variable in their experiment: 

• What factor are we trying to test? 

Dependent Variables  

The dependent experiment variable is what the scientist uses to measure the effect of the changes to the independent variable. The dependent variable depends on the independent variable. 

Ask your students the following question to determine the dependent variable in their experiment: 

• What factor will we use to measure the progress of our test? 

Controlled Variables

The controlled experiment variable is a factor that is not being examined in the experiment. The scientist will keep the controlled variables constant so that their effect on the test is minimized. 

Ask your students the following question to determine the controlled variable in their experiment:

• What factors do we need to keep constant so that they will not affect our results? 

You can use the handy infographic below to help determine your experiment variables.

A Look At A Sample Project 

Question

Which soil is best for house plants to be grown in? 

Hypothesis

If a plant is grown in potting soil, then it will grow much faster. 

Experiment Design

I will begin by filling three pots with soil from my backyard, which I will call my control group. Then, I will fill three more pots with potting soil from the store, which I will call test group #1. Finally, I will fill three more pots with sand from the sandbox, which I will call test group #2. Next, I will plant one tablespoon of grass seed in each pot. I will water each of the pots with a nutrient-rich solution made from fertilizer and water on the first day. After that, I will set each pot on a windowsill in full sunlight. I will check the pots daily for four weeks and water them with the nutrient-rich solution when the soil appears dry. Once I notice that the plants have sprouted, I will record how much they grow each day until the end.

Experiment Variables

The student with the above experiment design would have the following variables: 

• Independent Experiment Variable: the type of soil 

• Dependent Experiment Variable: the growth of the plant 

• Controlled Experiment Variables: the amount of sunlight, the amount of water, the size of the pot, the type of plant 

I hope that this gives you a clearer picture of experiment variables. If you still have questions, hit the email icon and send them our way!