Quasi–Experimental Design in Psychology

We put a 'quasi' before the experimental investigation because this type of design looks like an 'as-if' but not a real exploratory design. For a true exploratory study, there is a process called random assignment: researchers have total control and knowledge over how the investigation subjects will be assigned to the investigation group. Normally, it is a random process, and the treatment and control groups are statistically comparable before the treatment.

In other words, we have eliminated any prior selection bias. However, researchers need to learn the assignment process, and the treatment and control groups may be statistically different and not directly comparable. We rely on reasonable assumptions and investigation design to eliminate selection bias. Any quasi-exploratory plans contain a section that describes how they eliminate selection bias. For example, the most popular quasi-exploratory design, difference-in-differences, relies on the parallel trend assumption between the treatment and control group to draw valid inferences.

What is Quasi Experimental Design?

The experiment is done after the groups have been created, quasi-experimental designs are known as ex-post-facto or after-the-fact experiments. Because the independent variable has already occurred, the experimenter investigates the influence after the variable's occurrence.

For example, if we want to investigate gender variations in verbal learning figures, we would have to do a quasi-experiment because we cannot randomly assign participants to male or female circumstances. We cannot form new organizations of men and women but must instead draw from existing ones. In other words, in pseudo experiments, we do not modify variables but instead watch groups of participants. Instead of randomization, matching is utilized.

Types of Models

Major types of models are −

  • Group Design for Non-Equivalents − Non-equivalent sample models can be thought of as combining either genuine and developed a semi investigation. It utilizes both of its strengths, which is the reason. Employs the pre-existing categories comparable to those in a real trial, namely the treatment and placebo categories. However, it does not have the randomness that a quasi-experiment does. Investigators make sure while categorizing that their findings are not affected by any third factors or extraneous factors.

    The groupings are, therefore, as comparable as they can be. We may choose groups that are more comparable to one another, similar to how we discussed the sociopolitical investigation. When measurements for the already-existing categories are accessible and can be matched with the experimental group, a regressed position displaced (RPD) method is utilised.

  • Regression Point Displacement (RPD) − For bigger organizations in general, such as cities or businesses, this strategy has several advantages. A smaller comparative component is used in RPD to compare a particular software component.

Types of Quasi Experimental Design

There are several quasi-experimental designs, each with a unique set of uses in a certain setting. In this section, we will look at various notable quasi-experimental designs.

Non-Equivalent Group, Post-test only Design

The non-equivalent, post-test-only approach involves administering an outcome measure to two groups: a program/treatment group and a comparator group. For example, one set of students may receive reading teaching through a whole language curriculum, while the other group receives reading instruction through a phonetics-based approach. A reading comprehension test can be conducted after twelve weeks to determine whether the program was more successful. A key issue with this method is that the two groups may be different before any training takes place and may differ in significant ways that determine how much reading development they can accomplish.

For example, suppose it is discovered that students in phonetics groups do better. In that case, there is no way of knowing whether they were better prepared or better readers before the program and whether other variables contributed to their improved performance.

Non-Equivalent Control Group Design

A control group and an experimental group are compared in this design. However, the groupings are chosen and assigned for reasons other than randomness. The issue with this design is establishing how to compare the experimental and control groups' findings. For example, we want to examine the impact of special training programs on the grade point average of 10th-grade pupils.

The researcher could not pick a random sample because the school would not allow the experimenter to reassemble the classes. As a result, the researcher chose two sections of X-grade students from the same school. Because the patients were not randomly assigned to the two groups, we cannot assume that the groups were comparable prior to the experimental modification. We find out the grade point at the beginning of the program and again at the end. Our control group is the group that does not get treatment (training).

The Double Pre-Test Design

This is a very robust quasi-experimental design in terms of internal validity. Because in a pre-post non-equivalent group design, the non-equivalent groups may differ in some way before the program is administered, and we may mistakenly ascribe post-test differences to the program. Although the pre-test aids in determining the degree of pre-program similarity, it does not tell us if the groups change at comparable rates prior to the program. Prior to the program, the double pre-test design contains two measurements. As a result, if the program and comparison group mature at different rates, we may identify this as a difference between pre-test one and pre-test 2. As a result, its design specifically addresses selection maturation risks.

The Switching Replications Design

Internal validity is likewise quite robust in the Switching Replications quasi-experimental approach. It may also improve external validity or generalizability because it allows for two distinct program implementations. The design consists of two groups and three measurement periods. Both groups are pretested in the initial step of the design, one is given the program, and both are post-tested. The program is supplied to the original comparison group in the second phase of the design, while the original program group serves as the "control." This design is structurally identical to the randomized experimental variant but lacks a random assignment to a group. It is unquestionably better than the straightforward pre-post non-equivalent group design.

Difference between Quasi-Experimental Design and True Experimental Design

The experimenter has total control over the experiment in a real experimental context. The experimenter has no control over the assignment of the subject to the condition in a quasi-experimental circumstance. In a real experimental design, variables are manipulated; however, in a quasi-experimental design, variable manipulation is not feasible; instead, we observe categories of individuals.

For example, if we wish to explore the influence of gender, we cannot alter gender; instead, we classify groups based on what we believe is the most significant difference between them. We provide several independent variables to two pre-existing groups in a pseudo-experimental approach. We may need to determine whether the behavior difference was caused by group differences or by the independent variable. A quasi-experiment allows for further differences between the experimental and control circumstances, allowing for other possible differences to persist.


Like an exploratory setup, a quasi-exploratory approach seeks to prove a connection between someone's independent and dependent variables. Such an -experiment, therefore, somehow does not depend upon random selection, unlike an investigation conducted. Rather, non-random factors are used to classify people. Developing semi-planning is useful when real trials cannot be undertaken for moral or situational factors. Despite the quasi-exploratory investigation, strategies are often used in information systems research; however, more is needed about their advantages and disadvantages.

According to the comparative rank and terminology of developed semi-investigation designs described in this work, certain models are more likely than others to allow for deterministic explanations of interaction effects. The advantages and disadvantages of the investigation design must be emphasized in model-based approaches from a quasi-exploratory investigation. Future researchers in information systems should select the most robust architecture that is practical given the unique conditions.

Updated on: 10-Apr-2023


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