RESEARCH: Quasi Experimental Research Design

Summary

This video script from the English Simplified channel delves into quasi-experimental research design, a method aiming to establish cause and effect without random assignment. It's used when true experiments are impractical or unethical. The script outlines five types of designs, including post-test only, pre-test post-test, interrupted time series, and switching replications, each with unique procedures and data analysis methods. The goal is to provide clarity on when and how to apply these designs in real-world settings.

Takeaways

• 🧪 Quasi-experimental designs aim to establish cause and effect relationships, similar to true experiments, but without the use of random assignment.
• 🔄 Unlike true experiments, quasi-experiments do not use random sampling or random assignment, which is a method of placing participants into different treatment groups randomly.
• 🚫 Quasi-experimental designs are often used when it is unethical or impractical to conduct a true experiment, typically in field settings where random assignment is difficult.
• 👥 Quasi-experiments involve at least two groups: a control group and an experimental group, but participants are not selected through random sampling.
• 📝 There are five main types of quasi-experimental designs: post-test only non-equivalent groups, pre-test post-test non-equivalent groups, interrupted time series with non-equivalent groups, pre-test post-test with switching replication, and switching replication with treatment removal.
• 📊 Post-test only non-equivalent groups design involves a treatment given to one group and a comparison of post-tests between the experimental and control groups.
• 📉 Pre-test post-test non-equivalent groups design measures the dependent variable before and after treatment, comparing means or using statistical tests like t-test for analysis.
• 🕒 Interrupted time series design involves measurements taken at intervals over time, both before and after an intervention in non-equivalent groups.
• 🔄 Pre-test post-test with switching replication administers treatment to one group first, then switches to the control group, analyzing the dependent variable's changes.
• 🔄 Switching replication with treatment removal design involves phases where treatment is given and then removed for one group while the other group receives it later, analyzing the effects of treatment presence and absence.
• 🔑 The key difference between quasi-experimental and true experimental designs is the absence of random selection and assignment in quasi-experiments, which affects the internal validity of the research.

Q & A

What is the main difference between a quasi-experimental design and a true experiment?

The main difference is that a quasi-experimental design does not rely on random assignment of subjects to groups, unlike a true experiment which uses random sampling and assignment.

Why is quasi-experimental research used instead of a true experiment?

Quasi-experimental research is used in situations where it would be unethical or impractical to run a true experiment, often in field settings where random assignment is difficult or impossible.

What are the two groups typically involved in quasi-experimental designs?

The two groups typically involved are the control group and the experimental group.

How does the post-test only non-equivalent groups design differ from the pre-test post-test non-equivalent groups design?

In the post-test only non-equivalent groups design, there is no pre-test, and only the experimental group receives the treatment before the post-test. In contrast, the pre-test post-test non-equivalent groups design includes both a pre-test and a post-test for both groups, with the experimental group receiving the treatment in between.

What is an interrupted time series design with non-equivalent groups?

It is a variant of the pre-test post-test design where measurements are taken at intervals over time, both before and after an intervention in two or more non-equivalent groups.

How is the pre-test post-test design with switching replication applied?

In this design, a pre-test is administered to both groups, then one group receives a treatment while the other does not. After assessing the dependent variable again, the treatment is added to the control group, and the dependent variable is assessed one last time.

What is the purpose of the switching replication with treatment removal design?

This design is used to assess the effects of both the introduction and removal of a treatment by administering it to one group first, then to the other group, and analyzing the dependent variable's changes over time.

How is data analyzed in a post-test only non-equivalent groups design?

The data is analyzed by comparing the post-test results of the two groups, which includes the experimental group that received the treatment and the control group that did not.

What statistical analysis is often used in the pre-test post-test non-equivalent groups design?

The data is often analyzed using a t-test to compare the mean of the post-test results between the two groups.

How does the interrupted time series design with non-equivalent groups help in understanding the impact of an intervention?

This design helps by providing a series of measurements over time, allowing for the analysis of trends and the impact of the intervention at different points in time for both the experimental and control groups.

What is the significance of random sampling and random assignment in true experimental research?

Random sampling and assignment are crucial in true experimental research to reduce bias and ensure that the results can be generalized to the population, establishing a stronger cause-and-effect relationship.