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Research Designs: Quasi-Experimental, Case Studies & Correlational Research Designs

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  • 0:05 Research Without a…
  • 0:53 Quasi-Experimental Research
  • 4:39 Case Studies &…
  • 7:07 Lesson Summary
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Lesson Transcript
Instructor: Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

The true experiment is not the only way to conduct research. This lesson will help you understand the use of quasi-experimental research designs, case studies, and correlational research.

Research Without a True Experiment

Imagine we want to know if eating carrots is related to eyesight in some way. We do not have the opportunity to perform a true laboratory experiment, so how will we go about researching this idea?

There are many different ways we can go about finding the answer to this question: we can examine existing information to look for data that can be manipulated to show possible relationships, we can observe what we see in the world around us, or we can examine specific groups. The research can be simple or complicated. It can take a long time and be expensive, or it can occur relatively quickly with low costs.

Let's look at some of the common research designs that could be used to determine the relationship, if any, that exists between eyesight and eating carrots.

Quasi-Experimental Research

First let's look at quasi-experimental research. Quasi-experimental means that the research will include features of a true experiment but some elements may be missing. The most common experimental element to be missing is a random sample. A random sample occurs when every individual in the group being studied has an equal chance of being selected. Without a random sample, it is more difficult to demonstrate cause and effect links in research.

Even with the possibility of interpretation problems, in human growth and development research, quasi-experimental research is a common and often necessary replacement for a true experiment. This is usually because it is not practical or ethical to utilize a random sample. For example, imagine trying to create a random sample for a study on the effects of child abuse among single parents. If a person is randomly selected from a group of single parents to be part of the experimental group, they will be forced to abuse their children throughout the study. This would definitely not be acceptable!

Quasi-experimental research cannot illustrate cause and effect relationships as accurately as a controlled experiment. However, cause and effect relationships can be inferred from the data. Just keep in mind that there can be a larger margin of error for these assumptions, and that the margin of error can vary between studies.

Types of Quasi-Experimental Research

Now we will examine three types of quasi-experimental research: cross-sectional, longitudinal, and cross-sequential. Cross-sectional research studies make a comparison of different groups at the same time. In human growth and development, cross-sectional research is most often used to look at different groups of people at different ages.

Thinking of our carrots and eyesight scenario, an example would be a study where kids who eat carrots and kids who do not eat carrots are separated into groups. Let's say we want to see how many of these children are wearing glasses at the ages of 2, 5, and 10. We would have six total groups - one for each age group who eats carrots and one for each age group who does not eat carrots. Conclusions about the effect of eating carrots on eyesight would be based on the information gained from these six groups.

Cross-sectional research is most often used because of the ability to get quick results. This is because you are looking at different, but similar, groups instead of waiting for the original group to change.

Longitudinal research studies look at one individual or one group over a period of time. An example of longitudinal research would be a study where a group of two-year-old children are separated into those who eat carrots and those who do not. These two groups of children are examined at the ages of 2, 5, and 10. Conclusions about the effect of eating carrots on eyesight would then be based upon the information gained from these two groups.

Longitudinal research typically takes a much longer period of time to get results. It can also be expensive or difficult to track study groups for long periods of time. Because of this, it is used less often.

Cross-sequential research studies compare two separate, but similar, longitudinal research studies that are done at different times. Remember the longitudinal research example, where we followed two groups of children for eight years, to see if we found a relationship between their carrot eating habits and eyesight? In order to perform a cross-sequential research study, this would have to be done twice and at different periods of time. This means it could take up to 16 years just to get the data.

As you might imagine, cross-sequential research studies are much more complicated, expensive, and time consuming than other research designs. Because of this, it is seldom used, even though it is a very effective way of collecting useful data.

Case Studies and Correlational Research

In human growth and development research, case studies and correlational research are also often used. These types of studies must be carefully conducted so that the data obtained has validity. Validity is a term that refers to whether or not a study measures what it is supposed to measure.

It is important to remember that this type of research can only be used to describe what is being seen. No cause and effect relationship can be inferred from the observations. It is also important to be aware of any personal bias on the part of the observer.

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