Quasi-experimental research: what is it and how is it designed?

Quasi-experimental research is a type of research widely used in psychology. Its most relevant feature is that experimental groups are not selected at random, but already formed groups (eg a football team) are chosen.

It is based on a descriptive methodology and some quantitative and qualitative elements, and is used to study different behaviors, social variables, etc. In this article, we will learn about its characteristics and some differences with experimental research, as well as the advantages and disadvantages that it has.

    What is quasi-experimental research?

    Quasi-experimental research is used in particular in the field of psychology, but also in the social sciences. It’s a type of research halfway between experimental research and observational research. In fact, many authors do not consider it to be scientific, although it has notable advantages, as we will see in this article.

    Unlike experimental research, in quasi-experimental research the degree of control of strange variables (VVEE) is lower. For their part, the strange variables are the variables or factors that produce an effect on the variable that we are studying (dependent variable), but that we must control, because its effect is different from that produced by the variable (s). independent (s) (which are the ones we want to study).

    How do we investigate?

    But how is this really investigated? Both in quasi-experimental research and in other types of research, both in psychology and in other sciences, research it is mainly based on the study of the effect of one independent variable (VI) (or more) on another variable, Dependent variable called (RV) (or more).

    For example, we investigated when we want to study the effectiveness of a treatment (independent variable) in reducing anxiety (dependent variable).


    Quasi-experimental research it has its origins in the field of education. It arose from the observation that some effects or phenomena could not be studied using the experimental method and had to use alternative designs. These were mainly social phenomena or variables.

    In recent years, the number of studies conducted as part of quasi-experimental research has increased.


    There are certain characteristics that differentiate quasi-experimental research from other types of research. They are as follows.

    1. Non-random

    The basic characteristic of quasi-experimental research (and this is the difference between real research) is non-random in the formation of experimental groups. In other words, the researcher selects already formed groups (for example, students in a course or office workers) to conduct their experiment.

    In addition, this type of research is used when subjects cannot randomly assign to different experimental conditions Of research.


    To illustrate, let’s take an example: imagine that we want to study the effectiveness of three types of psychological therapy (eg, psychodynamic, cognitive-behavioral, and systemic) in reducing the level of anxiety in a group of people.

    If we were to use an experimental and not a quasi-experimental design, we would assign the subjects to the different experimental conditions (in this case, the three types of therapy) at random, i.e. using chance.

    In quasi-experimental research, on the other hand, we couldn’t do that. To resolve this problem, it is often chosen to include a control group in the experiment.

    2. No secondary systematic variance control

    On the other hand, quasi-experimental research it is also a good option when the secondary systematic variance cannot be controlled; it arises when the internal validity of the experience is threatened. Internal validity is what ensures that the independent variable is the cause of the dependent variable (i.e. has an effect on it).


      When a quasi-experimental type of research is used, and not having selected the experimental groups at random, one thing happens: that we cannot guarantee that all subjects have similar characteristics. In other words, there is less control over the variables. This makes the results less reliable (hence the name “quasi” experimental).

      This means that this type of research is not used as much in laboratory settings., But rather in natural contexts, in schools, etc. In other words, it is mainly used in applied research.

      Thus, quasi-experimental research has both positive and negative components. Let’s look at its pros and cons.


      The main advantage of quasi-experimental research is that allows you to select accessible and already formed groups; furthermore, it is often difficult to find groups that meet all the requirements to participate in an experiment (as would happen in an experimental design).

      On the other hand, they are easy to apply and economical in design. The preparation time they need and the resources to be allocated are less than in an experimental design. In addition, it is a type of research that can be applied not only to study groups, but also to individual cases.


      As negative characteristics or drawbacks of quasi-experimental research, we find their lower precision and validity compared to experimental models.

      In addition, the lack of randomness in the formation of groups poses a threat to the validity of the experiment and to the precision or accuracy of the experiment.

      On another side, often in such experiments, the so-called placebo effect occurs, Which consists of feeling or perceiving an improvement after believing that we have received a treatment (which we have not actually received).

        Types of designs

        In quasi-experimental research, particularly in the field of psychology, two types of quasi-experimental conceptions are particularly used:

        1. Cross-sectional drawings

        From these drawings different groups are studied at a specific time. For example, we can use them to measure the IQ of a grade 4 ESO class on January 1.

        In other words, this type of design is based on collecting data at a given time (all at once). The goal is to describe and analyze a number of variables.

        2. Longitudinal drawings

        This second type of designs, the longitudinal ones, they study how certain variables (or only one) evolve or change in a group of subjects (or more). In other words, they study these variables at different times. For example, in January, February and March (although this could also be with time intervals of years or more).

        They can also be applied individually for unique cases. The goal is to study the change that occurs in time period “X”.

        Bibliographical references:

        • Balluerka, N. and Vergara, AI (2002). Models of experimental research in psychology. Madrid: Prentice-Hall.
        • Fonts de Gràcia, S. García, C. Quintanilla, L. et al. (2010). Fundamentals of research in psychology. Madrid: UNED.
        • Shadish, WR, Cook, TD and Campbell, DT (2002). Experimental and quasi-experimental models. Boston: Houghton Mifflin Company.

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