Designing an Experiment to Test a Given Hypothesis

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  • 0:01 What Is a Hypothesis?
  • 1:05 Identifying Variables
  • 2:26 Controlling for Other Factors
  • 3:24 Parameters of the Experiment
  • 5:44 Putting It All Together
  • 7:01 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

A well-written hypothesis is the key to any well-designed experiment. In this lesson, we'll work through the process of designing an experiment based on the hypothesis it's meant to test and see how the two work to complement each other.

What Is a Hypothesis?

By now, you should be pretty familiar with the idea of a hypothesis. This is a proposed explanation for scientific observations. And what's really important about a hypothesis is that, when written correctly, it helps create a well-designed experiment.

The two go together like peanut butter and jelly, movies and popcorn, and rock and roll. They not only complement one another but are also specific to each other. This is because an experiment is specifically designed to test a given hypothesis. Experiments are certainly fun to perform, but that's just a bonus for us! Their main purpose is to see whether our predictive statements, our hypotheses, are supported or not.

But even with a solid hypothesis, designing an experiment isn't always easy because there's a lot to take into consideration. So, let's take a look at the process to see how we would go about setting up our experiment based on what we're trying to test.

Identifying Variables

Say that you are a pet store owner and want to know what kind of fish food the goldfish you sell prefer so that you can recommend this to your customers. You have three different foods that you can test in this experiment, and a good hypothesis for your experiment might be: When the goldfish are offered the three different foods, they will prefer food A.

This is a good hypothesis because it meets a number of criteria. First, it's a clear statement that is testable. Second, it's a predictive statement - you have decided which food you think the fish will prefer and said so in your statement. Finally, not only can this be tested, but it can be done in one experiment. You won't need to tag on other experiments to complete the process; this should be pretty straightforward.

You've also done something else in that hypothesis, which is very important for your experiment - you've identified measurable variables. In this experiment, the food choice is the independent variable because this is the variable that is manipulated during the experiment. It's the one you change in order to get some results, but it's not tied to anything else in the experiment - it's independent.

The food preference is therefore the dependent variable because it is the variable that is affected during the experiment. The choice of food is dependent on the variety you present, which is how this type of variable gets its name.

Controlling for Other Factors

One more thing that you haven't explicitly defined but that you'll need to take into careful consideration when designing your experiment is your control variables. These are any variables that are controlled during and between experiments. What we mean by this is that they are the same for all the subjects in the experiment - in our case, the goldfish.

We control for these other factors because they could affect the dependent variable and may influence the experimental results. For example, the water temperature, amount of light, time of day the feeding occurs, amount of food given, and order of food type presented could all have an effect on the preference of food our goldfish have. So, to make sure that the only thing they're preferring is the food itself (not when they get it or how much they get each time), we set these other variables the same for all the goldfish, and this ensures that our experiment is testing only what we want it to test.

Parameters of the Experiment

Okay, so now that you've got your variables set up, let's figure out how you're going to run this experiment. Luckily, you have a lot of extra aquariums sitting in back of the store, so you can test a bunch of fish individually in their own tank. This is important because if you have more than one fish in each test tank, you can't know which foods were eaten by which fish, so you can't determine if there was a preference or not.

So, you've separated 50 goldfish into 50 separate tanks. Each tank has the same amount of water coming from the same source, and it will be kept at the same temperature and in the same amount of light throughout the day. You've also put barriers between each tank so the fish don't see each other and possibly intimidate one another into not eating (yet another variable that needs to be controlled for).

You've decided on a set amount of food to feed each fish and that you will feed each fish twice a day - once at 7:00 AM and again at 7:00 PM. You will also offer each fish the same amount of all three foods at the exact same time, so that you don't assume that the first food they get is the preferred one, when in reality they may have just gotten too full to eat the other foods presented second and third.

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