The word ‘quasi’ means resembling. Thus a quasi-experimental design is one that resembles a true experiment but lacks some of its key characteristics. It is a quantitative research procedure where the researcher must select subjects of research from preexisting groups to conduct their study. The key characteristics that distinguish an experiment from a quasi-experimental design are that in a true experiment, the researcher has full control of the study, while in a quasi-experimental, the experimenter lacks control of the study. Also, a true experimental design involves the manipulation of variables contrary to a quasi-experimental, where the researcher cannot manipulate the variables but instead observes the categories of the subjects under study.

Types of Quasi-Experimental Design

Research designs are used to assess the effectiveness of an action, for example, health programs or educational practices. There are multiple kinds of quasi-experimental research designs. The types of quasi-experimental design include:

(1). Non-Equivalent Group, Posttest-Only Design

The non-equivalent group, posttest-only design of quasi-experimental research design involves measuring the results of two groups where only one of the groups has undergone the treatment. For example, a professor can choose two of their classes and administer different learning programs to each. One group of students can learn through online classes, while the others can use physical classes. After a month or two, they can administer tests to see which method is more effective in delivering results.

(2). Non-equivalent Control Group Design

In the non-equivalent control group design, the researcher compares a control and an experimental group. The groups are not randomized but are chosen out of convenience. In this design, for example, the professor would use the teaching method under study on only one group of students and then measure the results after the preferred period to measure its effectiveness.

(3). Interrupted Time Series Design

The interrupted time series design allows the same group under study to be compared over time by assessing the trend before and after they are subjected to treatment. In this design, pre-testing and post-testing are done at intervals. For example, a researcher may want to hold a campaign to reduce alcohol consumption in a group of people in October. They would collect data on people drinking before October, then hold the campaign and continue collecting data after October. The researcher can identify the trend in alcohol consumption rates before and after the campaign to assess whether it had an impact.

(4). Multiple Time Series Design

In the multiple time series design, there are two groups under research. One group gets treatment, and the other is not subjected to treatment and acts as a control. The multiple time series quasi-experimental research design is mostly used in complex settings.

(5). Repeated Treatment Design

The repeated treatment design is a quasi-experimental research method where a group of participants is exposed to multiple conditions of the same variable. Through evaluating the effects of the repeated administration of the treatment, the researcher identifies the effects of both variables on each other. A major advantage of the repeated treatment design is that it ensures accuracy by preventing the range of individual differences.

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