What Is an Experiment? Definition and Design

The Basics of an Experiment

An experiment is a test designed to evaluate a hypothesis or theory.
An experiment is a test designed to evaluate a hypothesis or theory. Hero Images / Getty Images

Science is concerned with experiments and experimentation, but do you know what exactly an experiment is? Here's a look at what an experiment is... and isn't!

Key Takeaways: Experiments

  • An experiment is a procedure designed to test a hypothesis as part of the scientific method.
  • The two key variables in any experiment are the independent and dependent variables. The independent variable is controlled or changed to test its effects on the dependent variable.
  • Three key types of experiments are controlled experiments, field experiments, and natural experiments.

What Is an Experiment? The Short Answer

In its simplest form, an experiment is simply the test of a hypothesis. A hypothesis, in turn, is a proposed relationship or explanation of phenomena.

Experiment Basics

The experiment is the foundation of the scientific method, which is a systematic means of exploring the world around you. Although some experiments take place in laboratories, you could perform an experiment anywhere, at any time.

Take a look at the steps of the scientific method:

  1. Make observations.
  2. Formulate a hypothesis.
  3. Design and conduct an experiment to test the hypothesis.
  4. Evaluate the results of the experiment.
  5. Accept or reject the hypothesis.
  6. If necessary, make and test a new hypothesis.

Types of Experiments

  • Natural Experiments: A natural experiment also is called a quasi-experiment. A natural experiment involves making a prediction or forming a hypothesis and then gathering data by observing a system. The variables are not controlled in a natural experiment.
  • Controlled Experiments: Lab experiments are controlled experiments, although you can perform a controlled experiment outside of a lab setting! In a controlled experiment, you compare an experimental group with a control group. Ideally, these two groups are identical except for one variable, the independent variable.
  • Field Experiments: A field experiment may be either a natural experiment or a controlled experiment. It takes place in a real-world setting, rather than under lab conditions. For example, an experiment involving an animal in its natural habitat would be a field experiment.

Variables in an Experiment

Simply put, a variable is anything you can change or control in an experiment. Common examples of variables include temperature, duration of the experiment, composition of a material, amount of light, etc. There are three kinds of variables in an experiment: controlled variables, independent variables and dependent variables.

Controlled variables, sometimes called constant variables are variables that are kept constant or unchanging. For example, if you are doing an experiment measuring the fizz released from different types of soda, you might control the size of the container so that all brands of soda would be in 12-oz cans. If you are performing an experiment on the effect of spraying plants with different chemicals, you would try to maintain the same pressure and maybe the same volume when spraying your plants.

The independent variable is the one factor that you are changing. It is one factor because usually in an experiment you try to change one thing at a time. This makes measurements and interpretation of the data much easier. If you are trying to determine whether heating water allows you to dissolve more sugar in the water then your independent variable is the temperature of the water. This is the variable you are purposely controlling.

The dependent variable is the variable you observe, to see whether it is affected by your independent variable. In the example where you are heating water to see if this affects the amount of sugar you can dissolve, the mass or volume of sugar (whichever you choose to measure) would be your dependent variable.

Examples of Things That Are Not Experiments

  • Making a model volcano.
  • Making a poster.
  • Changing a lot of factors at once, so you can't truly test the effect of the dependent variable.
  • Trying something, just to see what happens. On the other hand, making observations or trying something, after making a prediction about what you expect will happen, is a type of experiment.


  • Bailey, R.A. (2008). Design of Comparative Experiments. Cambridge: Cambridge University Press. ISBN 9780521683579.
  • Beveridge, William I. B., The Art of Scientific Investigation. Heinemann, Melbourne, Australia, 1950.
  • di Francia, G. Toraldo (1981). The Investigation of the Physical World. Cambridge University Press. ISBN 0-521-29925-X.
  • Hinkelmann, Klaus and Kempthorne, Oscar (2008). Design and Analysis of Experiments, Volume I: Introduction to Experimental Design (Second ed.). Wiley. ISBN 978-0-471-72756-9.
  • Shadish, William R.; Cook, Thomas D.; Campbell, Donald T. (2002). Experimental and quasi-experimental designs for generalized causal inference (Nachdr. ed.). Boston: Houghton Mifflin. ISBN 0-395-61556-9.
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Helmenstine, Anne Marie, Ph.D. "What Is an Experiment? Definition and Design." ThoughtCo, Apr. 5, 2023, thoughtco.com/what-is-an-experiment-607970. Helmenstine, Anne Marie, Ph.D. (2023, April 5). What Is an Experiment? Definition and Design. Retrieved from https://www.thoughtco.com/what-is-an-experiment-607970 Helmenstine, Anne Marie, Ph.D. "What Is an Experiment? Definition and Design." ThoughtCo. https://www.thoughtco.com/what-is-an-experiment-607970 (accessed June 4, 2023).