Quasi-experimental research is a type of research widely used in psychology . Its most relevant characteristic is that the experimental groups are not selected at random, but rather groups that have already been formed (for example, a football team) are chosen.

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

What is quasi-experimental research?

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

In contrast to experimental research, in quasi-experimental research the degree of control of extraneous variables (VVEE) is lower . In turn, the extraneous variables are those variables or factors that produce an effect on the variable that we are studying (dependent variable), but that we must control, since their effect is different from that produced by the independent variable(s) (which are the ones that we are interested in studying).

How do you investigate?

But how do you really investigate? Both in quasi-experimental research and in other types of research, whether in psychology or in other sciences, research is based above all on studying the effect of an independent variable (VI) (or more) on another variable , called a dependent variable (VD) (or more).

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


Quasi-experimental research has its origin in the educational field . It was born from the observation that some effects or phenomena could not be studied using the experimental method, and alternative designs had to be used. These were mainly social phenomena or variables.

In recent years, the number of studies carried out through quasi-experimental research has been increasing.


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

1. Non-randomness

The basic characteristic of quasi-experimental research (and that the difference from properly experimental research) is the non-randomness in the formation of the experimental groups . That is, the researcher selects groups that have already been formed (for example, students from a course or office workers) to carry out his or her experiment.

Furthermore, this type of research is used when subjects cannot be randomly assigned to different experimental conditions of the research.


To illustrate this, let’s think of an example: let’s imagine that we want to study the effectiveness of three types of psychological therapy (e.g., 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 quasi-experimental design, we would assign the subjects to the different experimental conditions (in this case, the three types of therapy) in a random way, that is, using chance.

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

2. No control of secondary systematic variance

On the other hand, quasi-experimental research is also a good option when the secondary systematic variance cannot be controlled ; this originates when the internal validity of the experiment 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 since the experimental groups have not been selected at random, one thing happens: that we cannot guarantee that all the subjects will have similar characteristics . In other words, there is less control of the variables. This makes the results less reliable (hence the name “quasi” experimental).

This implies that this type of research is not so much used in laboratory contexts , 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 advantages and disadvantages.


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

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


As negative characteristics or disadvantages in quasi-experimental research, we found its lower precision and lower validity, compared to experimental designs .

In addition, the lack of randomness in the formation of the groups threatens the validity of the experiment and the precision or accuracy of the experiment.

On the other hand, many times in this type of 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 really received).

Types of designs

In quasi-experimental research, specifically in the field of psychology, two types of quasi-experimental designs are especially used:

1. Cross-sectional designs

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

In other words, this type of design is based on collecting data at a specific time (in a unique time). The aim of this is to describe and analyse a series of variables.

2. Longitudinal designs

This second type of designs, the longitudinal ones, 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 it could be with time intervals of years, too, or more).

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

Bibliographic references:

  • Balluerka, N. and Vergara, A. I. (2002). Experimental research designs in psychology. Madrid: Prentice-Hall.
  • Fontes de Gracia, S. García, C. Quintanilla, L. et al. (2010). Fundamentals of research in psychology. Madrid: UNED.
  • Shadish, W. R., Cook, T. D. and Campbell, D. T. (2002). Experimental and quasi-experimental designs. Boston: Houghton Mifflin Company.