External validity is one of the main goals of researchers who want to find reliable cause-and-effect relationships in qualitative research.
When research has this validity, the results can be used with other people in different situations or places. Because without this validity, analysis can’t be generalized, and researchers can’t apply the results of studies to the real world. So, psychology research needs to be conducted outside a lab setting.
Still, sometimes they prefer to research how variables cause each other instead of being able to generalize the results.
In this article, we’ll talk about what external validity means, its types, and its research design methods.
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What is external validity?
External validity describes how effectively the findings of an experiment may be generalized to different people, places, or times. Most scientific investigations do not intend to obtain outcomes that only apply to the few persons who participated in the study.
Instead, researchers want to be able to take the results of an experiment and use them with a larger group of people. It is a big part of what inferential statistics try to do.
For example, if you’re looking at a new drug or educational program, you don’t want to know that it works for only a few people. You want to use those results outside the experiment and beyond those participating. It is called “generalizability,” the essential part of this validity.
Types of external validity
Generally, there are three main types of this validity. We’ll discuss each one below and give examples to help you understand.
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Population validity
Population validity is a kind of external validity that looks at how well the study’s results applied to a larger group of people. In this case, “population” refers to the group of people about whom a researcher is trying to conclude. On the other hand, a sample is a particular group of people who participate in the research.
If the results from the sample can apply to a larger group of people, then the study is valid for a large population.
Example: low population validity
You want to test the theory about how exercise and sleep are linked. You think that adults will sleep better when they do physical activities regularly. Your target group is adults in the United States, but your sample comprises about 300 college students.
Even though they are all adults, it might be hard to ensure the population validity in this case because the sampling model of students only represents some adults in the US.
So, your study has a limited amount of population validity, and you can only apply the results to some of the population.
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Ecological validity
Ecological validity is another type of external validity that shows how well the research results can be used in different situations. In simple terms, ecological validity is about whether or not your results can be used in the real world.
So, if a study has a lot of ecological validity, the results can be used in the real world. On the other hand, low validity means that the results can’t be used outside the experiment.
Example: low ecological validity
The Milgram Experiment is a classic example of low ecological validity.
Stanley Milgram studied authority in the 1960s. He randomly chose participants and directed them to employ higher and higher voltage shocks to penalize wrong-answering actors. The study showed great obedience to authorities despite fake shock and victim behaviors.
The results of this study are revolutionary for the field of social psychology. However, it is often criticized because it has little ecological validity. Milgram’s set-up was not like real-life situations.
In the experiment, he set up a situation where the participants couldn’t avoid obeying the rules. But the reality of the issue can be very different.
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Temporal validity
When figuring out external validity, time is just as important as the number of people involved and confusing factors.
The concept of temporal validity refers to how findings evolve. Particularly, this form of validity refers to how well the research results can be extended to another period.
High temporal validity means that research results can be used correctly in different times and places and that factors will be important in the future.
Example
Imagine that you’re a psychologist, and you’re studying how people act the same.
You found out that social pressure from the majority group has a big effect on the choices of the minority. Because of this, people act similarly. Even though famous psychologist Solomon Asch did this research in the 1950s, the results can still be used in the real world today.
This study, therefore, has temporal validity even after nearly a century.
Research methods of external validity
There are a lot of methods you can do to improve the external validity of your research. Some things that can improve are given below:
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Field experiments
Field experiments are like conducting research outside rather than in a controlled environment like a laboratory.
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Criteria for inclusion and exclusion
Establishing criteria for who can participate in the research and ensuring that the group being examined is properly identified
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Realism in psychology
If you want the participants to believe that the events that take place throughout the study are true, you should provide them with a cover story regarding the purpose of the research. So that they don’t behave any differently than they would in real life based on the fact.
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Replication
Doing the study again with different samples or in a different place to see if you get the same results. When many studies have been done on the same topic, a meta-analysis can be used to see if the effect of an independent variable can be repeated to make it more reliable.
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Reprocessing
It is like using statistical methods to fix problems with external validity, like reweighting groups if they were different in a certain way, such as age.
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Conclusion
As stated in the article, the ability to replicate the results of an experiment is a key component of its external validity. Using the sampling methods the external validity can be improved in the research.
Researchers compare the results to other relevant data to determine the external validity. They can also do the research with more people from the target population. It’s hard to figure out external validity in research, but it’s important to use the results in the future.
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