Assignment are used to allocate human participants or animal subjects to various groups in an experiment (e.g., a treatment group against a control group).* This guarantees that each participant or subject has an equal probability of being assigned to any of the groups. Participants are assigned at random, which ensures that any variations between and within groups are not systematic at the commencement of the experiment.

History of Random assignment:

In his “Illustrations of the Logic of Science” (1877–1878) and “A Theory of Probable Inference” (1879–1878), Charles S. Peirce stressed randomization in his statistical inference theory (1883). In the Peirce-Jastrow experiment on weight perception, Peirce used randomization.

To test volunteers’ capacity to differentiate weights, Charles S. Peirce randomly assigned them to a blinded, repeated-measures design. In the eighteen-hundreds, Peirce’s experiment inspired other psychologists and educators, who established a research tradition of randomized trials in laboratories and specialized textbooks.

Jerzy Neyman argued for randomization in survey sampling and experiments in 1923 and 1934. In his work on experimental design, Ronald A. Fisher argued for randomization (1935).

Random Assignment in Psychology:

In psychology experiments, random assignment refers to the use of chance processes to guarantee that each individual has the same probability of being allocated to any particular group. Individuals are allocated to one of many groups, such as the experimental group or the therapy group, randomly.

Tossing a coin, pulling names from a hat, spinning dice, or allocating random numbers to participants are all examples of random assignment.

It is vital to distinguish between random assignment and random selection. While random selection refers to how individuals are selected at random to reflect a wider population, random assignment deals to how those selected participants are subsequently allocated to an experimental group.

Random Assignment in Research:

Psychologists must conduct an experiment to see if changes in one variable lead to changes in another. Researchers frequently begin by formulating a testable hypothesis that predicts that one variable of interest will have an effect on another.

The independent variable is the variable that the experimenters will alter in the experiment, whereas the dependent variable is the variable that they will measure. While there are a variety of approaches to examining links between variables, an experiment is the most effective technique to determine whether or not two or more variables have a cause-and-effect relationship.

Random Assignment Example:

Consider the case of a researcher who wants to know if consuming caffeinated drinks before a test will help them perform better. Following the selection of a pool of participants at random, each person is allocated to one of two groups: control or experimental.

Prior to the exam, individuals in the control group are given a placebo drink that contains no caffeine. The experimental group, on the other hand, drinks a caffeinated beverage before to the exam.

Following that, participants in both groups take the exam, and the researcher compares the findings to see if the caffeinated beverage had any effect on test outcomes.

Importance of Random assignments:

The psychological research procedure relies heavily on random assignments. This procedure not only eliminates biasness, but it also makes it simpler to extrapolate the results of a sample group to a broader population.

Random assignment ensures that each group in the experiment has the same people, implying that the groups are more representative of the greater population. Psychology scholars may examine complicated events and contribute to our understanding of human nature and behavior by employing this method.

Random sampling versus random assignment:

Random sampling and random assignment are both significant ideas in research, but there is a distinction to be made.

Random sampling (also known as probability sampling or random selection) is a method of selecting participants from a population for your research. Random assignment, on the other hand, is a method of dividing the sample participants into control and experimental groups.

Random assignment is only used in between-subjects experimental designs. While random sampling is utilized in many types of investigations, random assignment is only used in between-subjects experimental designs.

Random sampling and random assignment are used in certain research, but either one or the other is used in others.

Because random sampling ensures that your sample is impartial and representative of the entire population, it improves the external validity or generalizability of your conclusions. This enables you to draw more robust statistical conclusions.

The internal reliability of the research is improved by random assignment, which assures that there are no systematic disparities between the people in each group. This allows you to conclude that the independent variable is to blame for the results.

What are some examples of how you may use a random assignment?

  • To utilize simple random assignment, begin by assigning a unique number to each member of the sample. Then, using computer systems or human techniques, allocate each individual to a group at random.

  • Use a computer program to generate random numbers from the list for each group using a random number generator.

  • Method of the lottery: Put all of the numbers in a hat or a bucket, then pick numbers at random for each group.

  • Toss a coin: When there are just two groups, flip a coin to determine whether each number in the list will be in the control or experimental group.

  • When you have three groups, roll a die for each number in the list to choose which group they will be in. Assume that rolling a 1 or 2 places them in a control group, a 3 or 4 places them in an experimental group, and a 5 or 6 places them in another control or experimental group.

Because each individual has an equal chance of being placed in any of your treatment groups, this form of random assignment is the most potent approach of placing participants in conditions.


Usage of random assignment:

  • To use simple random assignment, start by giving each member of the sample a unique number. Then, at random, assign each person to a group using computer systems or human procedures.

  • Using a random number generator, produce random numbers from the list for each group using a computer program.

  • The lottery’s method: Put all of the numbers in a hat or a bucket, and then choose a number for each group at random.

  • Flip a coin: When there are just two groups, toss a coin to see if each number in the list belongs in the experimental or control group.

  • Roll a dice for each number on the list to choose which group they will be in after you have three groupings.

Random assignment in block designs:

Random assignment is utilized only after individuals are sorted into blocks based on some feature in more elaborate experimental designs (e.g., test score or demographic variable). Because of these groups, a higher sample size is required to attain good statistical power.

A randomized block design, for instance, splits individuals into blocks based on a common feature (e.g., college students’ vs graduates) and then assigns individuals to each treatment condition using random assignment within each block. This allows you to determine whether the attribute has an impact on the treatment’s outcomes.

Blocking is used in an experimental matched design, and then individual participants from each block are matched up based on particular features. You assign each participant to one of the experiment’s conditions at random within each matched pair or group, then compare their results.

When is it not appropriate to utilize random assignment?

When simple random assignment is not appropriate or ethical, groups are assigned in a different method:

When contrasting two groups:

When comparing men and women, or persons with and without health issues, differences between participants might be the major focus of a study. Participants are not placed in groups at random; instead, they are placed in groups depending on their attributes.

The feature of interest (e.g., gender) is an independent variable in this sort of study, and the groups differ based on the different degrees of interest (e.g., men, women, etc.). All participants are assessed in the same way, and then their group-lead scores are calculated.

When it is not morally acceptable:

It is impossible to employ random assignment while examining harmful or risky activities. It is unethical, for instance, to randomly allocate individuals to one of two groups and urge them to consume big amounts of alcohol for your experiment if you are investigating heavy drinkers and social drinkers.

You can also perform a quasi-experimental research if you ca not allocate individuals to groups. In a quasi-experiment, you look at the results of pre-existing groups who are given treatments over which you may or may not have any influence (e.g., heavy drinkers and social drinkers). These groups are not chosen at random, but they may be compared when other variables are taken into account.


If simple random assignment is neither suitable nor ethical, groups are assigned using the different procedure:

  • When comparing and contrasting two groups.

  • When it is not ethically permissible.

Random Assignment versus Random Selection:

Random selection is the method for selecting a sample of persons from a population for your study. The method by which you assign the sample you draws to different groups or treatments in your study is known as random assignment.

In a research, both random selection and assignment are feasible. Assume you choose 100 clients at random from a pool of 1000 current clients. That is how random sampling or selection works. Let’s assume 50 of these customers are randomly assigned to a new extra therapy, while the other 50 are treated as controls. That was a completely random assignment.

Sampling is linked to random selection. As a result, it is mostly about the external validity (or generalization) of your findings. After all, we would use a random sample to ensure that our study participants are representative of the greater community.

Design is most closely tied to random assignment. In reality, we have an experimental design when we allocate volunteers to treatments at random. As a result, random assignment has the strongest link to internal validity. After all, we assign treatment groups at random to ensure that they are comparable (i.e., equal) before treatment.

Frequently asked Questions (FAQs):

Some frequently asked question asked by people are discussed below:

Q1. In a research, what is random assignment?

The assignment was chosen at random. Random assignment is a strategy used in studies to divide participants into several research groups with comparable characteristics so that the groups are equal at the start of the investigation.

Q2. What exactly is the purpose of a random assignment?

Participants are randomly assigned to groups, which ensures that any disparities between and within groups are not systematic at the start of the trial. As a result, any differences seen between groups at the end of the trial may be ascribed more definitely to the experimental techniques or therapy.

Q3. What is the condition of random assignment?

The procedure by which investigators pick participants from their overall sample to participate in a certain circumstance or group, with each participant having a specified chance of being allocated to each of the groups or conditions, is known as random assignment.

Q4. What role does random assignment play in determining cause and effect?

Experiments are the most effective method for determining cause and effect correlations between various factors. Confounding factors, or variables other than the independent variable, might cause a change in the dependent variable, hence randomly assigning participants helps to avoid them.

Q5. In an experiment, what is the objective of random assignment? Check all that apply.

The purpose of random assignment is to generate treatment groups that are comparable. If the groups are comparable, all changes in the dependent variables are related to treatment differences. Random assignment reduces the influence of confounding variables in this way.

Q6. What is the meaning of non-random assignment?

Methods for assigning research participants to treatment comparison groups that are not random, but are designed to generate groups that are similar.

Q7. What is the purpose of the quiz let with random assignments?

The goal of random assignment is to allow the experimenter to conceal the condition to which the participants were allocated.

Q8. What is the significance of random assignment in statistics?

Random assignment helps decrease the risks of confounding factors and alternative explanations by reducing the possibilities of systematic differences between groups at the start of an experiment. The procedure, on the other hand, does not always balance all of the confounding variables.

Q9. Which is more important: random assignment or random selection?

External validity, or the amount to which the researcher can generalize the study’s findings to a wider population, is thus dependent on random selection. Internal validity is dependent on random assignment, which allows the researcher to make causal claims regarding the effect of the treatment.

Q10. Is it possible to utilize random assignment in a questionnaire?

The method by which you assign the sample you draw to different groups or treatments in your research is taken as random assignment. In a research, both random selection and assignment are feasible. In a research, only one of these (random selection or random assignment) can be used but not the other.

Q11. Is it true that random assignment trumps random sampling?

We can create a sample that is typical of the population by using random sampling. As a result, the study’s findings may be applied to the broader community. We can ensure that the only difference between the various treatment groups is what we are looking at by assigning them at random.


In an experiment, random assignment or randomization, such as flipping a coin or using a random number generator, is used to assign human participants or animal subjects to different groups (e.g., a treatment group against a control group). This ensures that each participant or topic has an equal chance of being placed in one of the groups. Because participants are chosen at random, any differences between and between groups are not systematic at the start of the trial.

Random sampling (also known as probability sampling or random selection) is a technique for choosing study participants from a large group. In various sorts of research, random sampling is used.

Random sampling increases the external validity or generalizability of your results by ensuring that your sample is unbiased and representative of the total population. As a result, you will be able to make more reliable statistical findings.

The procedure for picking a sample of people from a population for your study is called random selection.


Advantages Disadvantages
Random assignment uses a chance process to assign subjects to experimental groups. its random nature tends to eliminate systematic differences
the process must have an equal probability of assigning a subject Sometimes random assignment is impossible because the experimenters cannot control the treatment


Project reporting based on the evaluated work. Homework is part of the assessment process in preparation for a degree.

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