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.
Finally, Connor and Emily will need to outline their procedures. They need to plan exactly what conditions the students will be in when conducting the experiment so that as many variables as possible are the same. For example, Connor and Emily cannot decide to test some students before lunch and some students after, or have a teacher conduct one experiment while Connor and Emily conduct another. It is important to keep as many elements the same as possible so that Connor and Emily can get as accurate results as possible. They contact the teachers and set up a time before lunch that they can conduct the experiment, as well as the rooms that they can use for the experiment. They prepare the materials ahead of time, labeling cups for the control group and the experimental group. They also label the cards 1 through 24 for each group, so they can track each child's preferences. (There are 24 students in each group because they've divided their sample of 48 in half to form the control and the experiment groups.) They make a list of all of the procedures they will use to conduct the experiment:
- Select groups by placing numbers into a hat (1 and 2).
- There should be 24 students in each group. Get absences from teachers.
- Group 1 goes to room 101 with Connor (the control group).
- Group 2 goes to room 102 with Emily (the experimental group).
- Explain to students that we want to know their beverage preference.
- Pass out the cards and explain the meaning of the thumbs-up, thumbs-down, and equal sign.
- Ask the students to take small sips of both before deciding their choice.
- Pass out the cups two per student according to the control and experimental groups.
- Ask students to sip their drinks and make a selection.
- Ask students to leave the cups on their cards and their hands in their laps as either Connor or Emily collects the information.
After carrying out the procedures to conduct the experiment, Connor and Emily can now review the information they've collected and analyze their data. What do you think the results are of the experiment? Do children prefer colored flavored beverages over clear?
When conducting an experiment, one of the most important elements of collecting information is the design of the experiment itself. To do this, you must first understand the concepts of control and treatment. The control is the group that remains untreated throughout the duration of the experiment. This was the group that had two cups of clear flavored drink in Connor and Emily's experiment. We next discussed treatment, which is the variable in an experiment that is used on an experimental group. This was the group that received one cup of clear liquid and one cup of colored liquid.
Remember, there are a few basic concepts 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.
Keeping these concepts in mind, you will be able to understand research and conduct your own experiments more efficiently! By the way, Connor and Emily did find that the students preferred colored liquids to clear!
As soon as you finish the video, perform these tasks:
- Remember the definition of experimental design
- Discuss the importance of having a control group
- Understand the necessity of a treatment in experimental design
- Detail the way in which an experiment can be designed