How Randomized Experiments Are Designed

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  • 0:01 What Is Experimental Design?
  • 0:40 Controls and Treatments
  • 2:00 Designing Your Experiement
  • 7:08 Lesson Summary
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Lesson Transcript
Instructor: Cathryn Jackson

Cat has taught a variety of subjects, including communications, mathematics, and technology. Cat has a master's degree in education and is currently working on her Ph.D.

When reading research or when conducting your own, it is important to understand the basic concepts of randomized experimental design that are covered in this lesson.

What Is Experimental Design?

Connor and Emily are working on their project for the school science fair. They want to know if children are more likely to enjoy a drink if it is an exciting color, rather than a clear flavored liquid. They need to design an experiment to explore this inquiry.

An experimental design is a plan for giving treatments to experimental groups and excluding control groups.

In this lesson, you will learn about how to design a randomized experiment in order to analyze inquiries and collect data. Before we get into designing Connor and Emily's experiment, you will first need to understand the concepts of controls and treatments.

Controls and Treatments

A good experimental design will have two basic elements: a control and a treatment.

The control is the group that remains untreated throughout the duration of an experiment. For example, if I wanted to know the effectiveness of a certain drug, I might have a control group that does not receive the drug. This way I can compare the group that takes the drug to the group that does not take the drug. If this group that does not take the drug improves, then I know it isn't the drug that was causing the improvement. The control group is the opposite of the experimental group, which receives the treatment.

Next, when designing an experiment, you will need a treatment, which is the variable in an experiment that is used on an experimental group. In the earlier example, we talked about finding the effectiveness of a certain drug. In this case, the treatment would be the drug that is given to the non-control group, or the variable.

Connor and Emily can design their experiment in a few different ways. However, they decide to get a clear, flavored beverage and give it to two groups. One group will get two cups of the clear, flavored beverage; this will be the control group. The second group will get two cups of the same clear, flavored beverage; however, one of the cups will have a little bit of coloring added. This will be the treatment group.

Now, let's talk about how Connor and Emily can design a randomized experiment.

Designing Your Experiment

Connor and Emily decide to use the children at a local elementary school to conduct their experiment, but before they can begin, they need to make a plan. Remember, this is called experiment design. It is important to note here that there are many types of experiment design depending on the type of research you are doing, the resources that are available, and the type of inquiry, or questions, that you may have. There are a few basic steps that you should keep in mind when designing any sort of experiment. They are: identifying the treatment, identifying the control, identifying the measures, selecting the sample, outlining the procedures, and conducting the experiment.

First, Connor and Emily have already identified their treatment (the colored flavored beverage) and their control (the clear flavored beverage). Now, they will need to identify how they are going to measure this experiment.

Remember that Connor and Emily have already hypothesized that children prefer a colored beverage over a clear beverage. To measure this preference, Connor and Emily created two cards: one has a thumbs-up and a thumbs-down, the other has an equal sign. Connor and Emily decide that they will ask the students to put their glasses on either the thumbs-up and thumbs-down card, with the preferred beverage on the thumbs-up; or they will put their glasses on the equal sign card, indicating that the beverages are either equally good or equally bad. Since they are looking for preference, this will allow them to see which children prefer the colored liquid over the clear or which children go by taste of the beverage, which will be no different. This is how Connor and Emily will measure the experiment, by comparing the number of preferred beverages to the number of disliked and equal beverages.

Next, Connor and Emily will have to select their sample. Now, they already know that they are using children from a local elementary school, but they don't have the time or the resources to give beverages to all of the students. This is where the random part of randomized experiment design comes in. Randomness is a good thing. Let's say that Connor and Emily decide to only experiment on the fifth graders. There is a possibility that fifth graders will have a better developed sense of taste and have no problem identifying that all of the liquids are the same. This would cause a problem in the experiment. By making a random selection, Connor and Emily can hope to avoid these problems.

There are many ways to conduct random sampling, so check out our lessons for more information! For this experiment, Connor and Emily pick the second, fourth, sixth, and eighth person in the alphabet in all of the classes, K through 5. There are two classes of each grade level, so that will give Connor and Emily a total of 48 students for their sample.

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