This article will define random assignment in psychological experiments. It will also discuss how it is different from random sampling or random selection.
What Is Random Assignment?
In psychology, random assignment is the utilization of procedures that rely on chance when it comes to experiments. This is done to ensure that every participant is given an equal opportunity at taking part in the experiment or to be assigned to a group.
In psychology experiments, there are different groups to which the participants can be assigned to. Those groups are generally the experimental and treatment groups. There are different ways that random assignments are achieved. Those methods include:
- Coin toss
- Drawing names
- Rolling a dice
- Assigning a number to participants
As you may notice, the methods are those that allow the researchers to assign the participants randomly.
Random Assignment and Random Selection
It is easy to confuse random assignment and random selection. The clue to their difference can be found in their names. Random selection refers to how participants of the experiment are chosen in a random manner. Random assignment, on the other hand, refers to the way that the participants are assigned to the different groups in the experiment.
This means it is possible to use random selection and random assignment in a single experiment. For example, researchers might be conducting an experiment dealing with the population of a school. They would need 100 participants for the experiment. The researchers can use random selection in picking the 100 participants from the overall population of the school.
The researchers can then use random assignment to pick 50 of the participants who will be part of the experimental group and the other 50 who will be the control group. Researchers use random selection to ensure that the participants they pick will be representative of the entire population.
For random selection, the researchers can also use the same methods employed in random assignment. When it comes to random selection, it’s important to remember that it is better to use larger samples because it is difficult to completely remove bias in the selection process and it can have a bigger impact on smaller groups.
Why Random Assignment Is Used
Well, just imagine an experiment in psychology where random assignment is not utilized. Let’s assume that in an experiment, 20 participants are invited to go to a venue. Since random assignment is not being used, the first ten to arrive will then be assigned to the control group and then the next ten will be assigned to the experimental group.
Do you see where the problem could in this situation be?
It will depend on what is being researched but at the end of the experiment can be attributed to the characteristics of the participants. Those who arrived early for example may share some attributes. Just as those who arrived later may have some characteristics between them.
So, now if the researchers will use a coin toss for assigning the group of a participant, then that means the shared attributes of the participants will have little to no effect on the results.
Issues with Random Assignment
The truth is that it’s impossible to guarantee that the groups will be matched. There will always be a difference between the two groups and their attributes will have an impact on the results. There is always the possibility that the random assignment will not separate the groups properly. In an experiment involving the academic performance of students, it is possible that the random assignment might group students who perform well academically in one group and students with poor academic performance in another.
How does random assignment work within a psychological experiment?
In psychology, researchers conduct experiments to determine if a change in one variable will also lead a change in another. For the experiments, they must come up with a hypothesis which states the change in variables that will happen in another.
The variable that the researchers will try to change is known as the independent variable. The dependent variable is the one which will they attempt to measure. An experiment is not the only way to check if there are connections between those variables but it is the best and it provides the most concrete results.
Here are the following steps to be taken by the researchers after they have formulated a hypothesis:
- They will conduct background research about the experiment. For example, they will need to review the related literature and make sure that the experiment has not been conducted before.
- Once the researchers are done with the preliminary research then they would pick the experimental design that they need to follow. The experimental design is basically the steps that they would be following for the research.
- The next step is for the researchers to pick the participants for the experiment. Ideally, they would use random selection which we have explained.
- Once the participants for the experiment have been chosen, it is time for them to be assigned to the groups that will be utilized for the experiment.
At this point, random assignment is going to be used by the researchers. It’s important that the participants should be assigned in a random way to make sure that the groups will be the same and that the results will not be biased.
In a psychological experiment like that, it is assumed that the two groups are the same at the beginning of the experiment so that any changes to it will be caused by the application of the independent variable.
Example of Random Assignment in an Experiment
Let’s say that a researcher was trying to find out if the consumption of a certain type of supplement right before an examination can have an effect on the performance of students. The researchers may try to randomly select students who will be participating in the experiment. For example, they can pick students from the same school who are about to take an exam. The students who are selected to participate can be assigned either in the control group or in the experimental group.
Once the groupings have been assigned, the researchers can then provide a supplement that will be studied. The students who are part of the control group will be given the placebo. That does not contain the substance to be studied. It’s important that the participants are not aware as to which group they belong to because that might have an effect on the results of the experiments.
The ones in the experimental group will be the ones given the actual substance being researched. All of the participants will then take the test and the results of each group will then be compared. That is when it will be determined if the variable has the effect as predicted in the hypothesis or not.
As you can see, random assignment is an important part of psychological research. It is one of the best methods for removing bias in a psychological experiment. On top of that, it makes the generalization of the results so much easier. With this technique, researchers can study complex human behavior and other phenomena.