Multiple Group Design: Definition & Examples

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  • 0:05 Experimental Design
  • 0:56 Levels of Variable
  • 2:27 Multiple vs. Two-Group Designs
  • 3:56 Assigning Subjects
  • 6:27 Lesson Summary
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Lesson Transcript
Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

What happens when a researcher has many groups in their study? In this lesson, we'll look closer at multiple-group design, including multiple-group design with independent groups and multiple-group design with correlated groups.

Experimental Design

Shakira is a psychologist who has been hired by an advertising agency. She needs to know what type of spokesperson works best to sell products to teenagers. Do ordinary people work better than celebrities? Should it be a teen or a parental figure? Or should companies just sell their products without a spokesperson at all?

Shakira has to decide how to answer those questions in an experiment. The process of making decisions about what type of experiment to run is called experimental design. There are many different ways that Shakira can organize her study and many different decisions she has to make as she is designing it. Let's work with Shakira to see what decisions she has to make and to look closer at one type of experimental design, the multiple-group design.

Levels of Variable

So, Shakira wants to know what type of spokesperson makes teenagers want to buy products. She decides that she'll gather teenagers and show them one of several different commercials for a product, and then let them decide if they want to buy the product or not. The commercial that results in subjects deciding to buy the product the most is the one that works best.

Pretty simple, right? But when Shakira goes to make the commercials for the study, she realizes she has a lot of spokesperson options: she has to make a commercial without any spokesperson, one with a non-famous person, one with a celebrity, and one with a parental figure. The levels of a variable are the different options of that variable. In Shakira's case, her independent variable (the spokesperson) has four different levels: none, non-famous, celebrity, and parental figure. Her dependent variable (sales) has two levels: the subjects can buy or not buy the product.

Think about the variable gender; it has two levels: male and female. Someone who is studying age might create three levels for that variable: young, middle-aged, and old. If letter grade is your variable, you might have five levels: A, B, C, D, and F. The point is that every variable has levels. Some have more than others, which brings us to the idea behind multiple-group designs.

Multiple vs. Two-Group Designs

Now, Shakira has a complicated study with four different levels of her independent variable. But what if she had a simpler design? What if she just wanted to know if having a spokesperson would make teens more likely to buy? In that case, she only has to make two commercials: one with a spokesperson and one without a spokesperson.

A two-group design in experiments involves having only two levels of your independent variable. Usually, this means a yes or no situation: yes, the commercial has a spokesperson, or no, it does not. But what about with Shakira's study with the four different levels? If an independent variable has more than two levels, it is called a multiple-group design. Usually, one of the levels is nothing at all and the other levels are variants. For example, Shakira has a no-spokesperson group, and then she has three different variants of a spokesperson: non-famous, famous, and parental.

Two-group and multiple-group designs are both valuable, but they answer different questions. A two-group design tells you whether your independent variable has an effect at all, while a multiple-group design tells you how much of an effect each level has. For example, if Shakira only wants to know if a spokesperson increases sales, she can go for a two-group design. But if she wants to know what level (or type) of spokesperson increases sales the most, she will opt for a multiple-group design.

Assigning Subjects

Let's go back to Shakira's original study. She wants to know which level of spokesperson has the biggest effect on sales, so she chooses a multiple-group design. That's it, right? She's ready to run her experiment! Well, not quite. She still has to decide which type of multiple-group design she wants to use. That's right; to make this more complicated, there are multiple types of multiple-group designs. But don't worry; we'll break each of them down.

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