How To Design a Science Fair Experiment

Design a Science Fair Experiment Using the Scientific Method

Science Fair Project
Middle school student explaining her science fair project to classmates. Ariel Skelley/Getty Images

A good science fair experiment applies the scientific method to answer a question or test an effect. Follow these steps to design an experiment that follows the approved procedure for science fair projects.

State an Objective

Science fair projects start with a purpose or objective. Why are you studying this? What do you hope to learn? What makes this topic interesting? An objective is a brief statement of the goal of an experiment, which you can use to help narrow down choices for a hypothesis.

Propose a Testable Hypothesis

The hardest part of experimental design may be the first step, which is deciding what to test and proposing a hypothesis you can use to build an experiment.

You could state the hypothesis as an if-then statement. Example: "If plants are not given light, then they will not grow."

You could state a null or no-difference hypothesis, which is an easy form to test. Example: There is no difference in the size of beans soaked in water compared with beans soaked in saltwater.

The key to formulating a good science fair hypothesis is to make sure you have the ability to test it, record data, and draw a conclusion. Compare these two hypotheses and decide which you could test:

Cupcakes sprinkled with colored sugar are better than plain frosted cupcakes.

People are more likely to choose cupcakes sprinkled with colored sugar than plain frosted cupcakes.

Once you have an idea for an experiment, it often helps to write out several different versions of a hypothesis and select the one that works best for you.

See Hypothesis Examples

Identify the Independent, Dependent, and Control Variable

To draw a valid conclusion from your experiment, you ideally want to test the effect of changing one factor, while holding all other factors constant or unchanged. There are several possible variables in an experiment, but be sure to identify the big three: independent, dependent, and control variables.

The independent variable is the one you manipulate or change to test its effect on the dependent variable. Controlled variables are other factors in your experiment you try to control or hold constant.

For example, let's say your hypothesis is: Duration of daylight has no effect on how long a cat sleeps. Your independent variable is duration of daylight (how many hours of daylight the cat sees). The dependent variable is how long the cat sleeps per day. Controlled variables might include amount of exercise and cat food supplied to the cat, how often it is disturbed, whether or not other cats are present, the approximate age of cats that are tested, etc.

Perform Enough Tests

Consider an experiment with the hypothesis: If you toss a coin, there is an equal chance of it coming up heads or tails. That is a nice, testable hypothesis, but you can't draw any sort of valid conclusion from a single coin toss. Neither are you likely to get enough data from 2-3 coin tosses, or even 10. It's important to have a large enough sample size that your experiment isn't overly influenced by randomness. Sometimes this means you need to perform a test multiple times on a single subject or small set of subjects. In other cases, you may want to gather data from a large, representative sample of population.

Gather the Right Data

There are two main types of data: qualitative and quantitative data. Qualitative data describes a quality, such as red/green, more/less, yes/no. Quantitative data is recorded as a number. If you can, gather quantitative data because it's much easier to analyze using mathematical tests.

Tabulate or Graph the Results

Once you have recorded your data, report it in a table and/or graph. This visual representation of the data makes it easier for you to see patterns or trends and makes your science fair project more appealing to other students, teachers, and judges.

Test the Hypothesis

Was the hypothesis accepted or rejected? Once you make this determination, ask yourself whether you met the objective of the experiment or whether further study is needed. Sometimes an experiment doesn't work out the way you expect. You may accept the experiment or decide to conduct a new experiment, based on what you learned.

Draw a Conclusion

Based on the experience you gained from the experiment and whether you accepted or rejected the hypothesis, you should be able to draw some conclusions about your subject. You should state these in your report.

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Your Citation
Helmenstine, Anne Marie, Ph.D. "How To Design a Science Fair Experiment." ThoughtCo, Feb. 16, 2021, Helmenstine, Anne Marie, Ph.D. (2021, February 16). How To Design a Science Fair Experiment. Retrieved from Helmenstine, Anne Marie, Ph.D. "How To Design a Science Fair Experiment." ThoughtCo. (accessed March 28, 2023).