Random Assignment: Definition With Examples

(Last Updated On: March 6, 2023)

Random assignment involves using procedures that rely on chance to assign participants to groups. Doing this means that every single participant in a study has an equal opportunity to be assigned to any group.

For example, in a psychology experiment, participants might be assigned to either a control group or an experimental group. Some experiments might only have one experimental group while others may have several treatment variations. Using random assignment means that each participant has the same chance of being assigned to any of these groups.

How Does Random Assignment Work?

So what type of procedures might psychologists utilize for random assignment? Strategies such as flipping a coin, assigning random numbers, rolling dice, and even drawing names out of a hat are commonly used.

The goal of a psychology experiment is to determine if changes in one variable lead to changes in another variable. Researchers will first begin by coming up with a hypothesis. Once researchers has an idea of what they think they might find in a population, they will come up with an experimental design and then recruit participants for their study.

Once they have a pool of participants that are representative of the population they are interested in looking at, they will then randomly assign the participants to their groups. Some participants will end up in the control group, which serves as a baseline and does not receive the independent variables. Other participants will end up in the experimental groups, which do receive some form of the independent variables.

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By using random assignment, the researchers make it more likely that the groups are equal at the start of the experiment. Since the groups are the same on other variables, it can be assumed that any changes that occur are the result of varying the independent variables.

After a treatment has been administered, the researchers will then collect data in order to determine if the independent variable had any impact on the dependent variable.

It is important to remember that random assignment is not the same thing as random selection. Random selection instead involves how people are chosen to be in a study. Using random selection, every member of a population stands an equal chance of being chosen for a study or experiment.

Examples of Random Assignment

Let’s imagine that you are a psychology researcher and you are doing an experiment to determine if getting adequate sleep the night before an exam results in better test scores. The researcher’s hypothesis is that participants who get 8 hours of sleep will do better on a math exam than participants who only get 4 hours of sleep.

The researcher starts by obtaining a pool of participants. She finds 100 participants from a local university. Half of the participants are female and half are male. She then assigns random numbers to each participants and uses a random number generator to randomly assign each number to either the 4-hour sleep group or the 8-hour sleep group.

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Those in the 8-hour sleep group agree to sleep for 8 hours that night while those in the 4-hour group agree to wake up after only 4 hours. The next morning, all of the participants meet in a classroom and everyone takes the same math test. The scores on the tests are then compared to see if the amount of sleep the night before had any impact on test scores.

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