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External Validity – Definition, Types & Research Methods

The concept of validity is now well-established in almost all research fields. According to this concept, a research study or test is valid if it measures what it claims to measure accurately and correctly. There are two types of validity, i.e., internal and external validity. As the topic line suggests, in today’s article, we will learn about the second type of validity. In this article, you will find information about its types and methods of measurement. However, before that, let’s define what this type of validity is.

What does it mean by external validity?

As the name suggests, this type of validity refers to outside the research study. External validity describes how effectively the research findings can be generalised to the overall population or people where the study is conducted. Most of the time, research studies do not wish to obtain outcomes that are correct for only a small portion of people or for only the respondents who took part in the study. Therefore, checking them for external validity is important. This validity is a big part of inferential statistics.

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An example of this can be a new drug which has been recently launched in the market. As a medical researcher, you do not want it to treat only the people who have taken it under the study. You want to use the results obtained for a bigger community and outside the experiment. To do this, you test the drug in the field and make it more generalised. This is what external validity is all about.

Types of external validity in research

Based on the focus of a research study, the researchers usually try to achieve three types of validity. The names of those three types are population, ecological, and temporal validity. Knowing the names is not enough to achieve this validity. Therefore, a brief description of the three major types of external validity is as follows:

1. Population validity

The first type of this validity is known as population validity. This type is related to the external population and measures how well the study’s results can be applied to a larger population. Remember that this population is outside the respondents that have been used during the study. If the research results can be applied to a large number of people, it means they are valid. If they cannot be generalised to the outer population, it means your study is not valid and needs some improvement somewhere. If you cannot measure this validity properly, do not forget to ask for help from dissertation writers UK.

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2. Ecological validity

The second type of external validity is called ecological validity. It is not about respondents or an outer population. Instead, this validity refers to how well the research results can be used in different situations other than the lab or research situations. Mostly, the researchers conduct research studies under controlled situations. In this type of validity, they expose themselves to different situations and see whether or not the results are the same.

3. Temporal validity

Lastly, when you are measuring the external validity of a research study, time is just as important as the number of people involved in research and other factors. The concept of temporal validity refers to how research results evolve with time. Particularly, this form of validity shows how well the research results can be extended to another period, and they remain the same for the same population.

Threats to measuring external validity

Making a research study and its findings externally valid is extremely important. But the threats to this validity make it difficult. Do you know what those threats are? No. Hence, a brief description of the major threats to external validity is as follows:

  • Sampling bias. This means selecting such a research sample which may or may not be representative of the research problem.
  • Experimenter effect. This threat comes from the researcher himself. It refers to the characteristics and behaviours of the researcher that may influence the study results.
  • Hawthrone effect. It is another potential threat to external validity. This effect is about the tendency to change behaviours when respondnets know they are being studied.
  • Situation effect. The situation of the research study also affects the validity. It comes from factors like setting, time, and location.
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Hence, these are the major threats to the external validity of research findings. As the researcher, you must know ways to counter them. However, if you do not know such ways, contact any PhD dissertation help in the UK. Their writers can help you a lot in this regard.


To sum up, external validity refers to how well your research results can be generalised to the overall population in a society. In this guidepost, we have discussed the three types of this validity and the threats. Hence, it is now your duty to know about all these things and act accordingly to reduce the threats.

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