Internal Validity: What it is in research + Examples

Internal validity refers to how confident you are in your research findings. It is one of the most essential aspects of scientific research and a key idea in understanding facts in general. You can only determine the accuracy of your research as a researcher if there are no factors that contradict your findings. It is the extent of confidence in the outcome. We’ll look at what internal validity is, why it’s important, and its examples in this post.

What is Internal Validity?

Internal validity in research is the method of verifying cause-and-effect relationships between your test situation and your research outcome. It also refers to the ability of research to rule out other causes for a result.

Confounding is a condition in which various factors interfere with the outcome of a research. The lower the chance of confounding in a study, the higher its internal validity. And from this, we can be more confident in the outcome.

In other words, if you can rule out other possible causes for your findings, then you can be sure that your research is internally valid. If your study meets the following three requirements, then you can only presume cause-and-effect:

  • The cause and effect change simultaneously.
  • In terms of time, the cause comes before the effect.
  • There are no other plausible reasons for the correlation you’ve found.


Internal validity further reveals that having the standard data helps a researcher to exclude irrelevant outcomes from the study. If the sample groups are correctly selected and measured, the relationship between the data will be acceptable.

The importance of internal validity

Researchers frequently attempt to establish clear relationships between the variables when they conduct experiments. Internal validity permits them to trust and believe the conclusions of a study’s causal relationship. When an experiment’s external validity is low, it cannot confidently demonstrate a causal relationship between variables under consideration. That’s why it matters in research. This can be one of the most powerful tools in research if applied correctly.

Internal Validity Threats

Internal validity threats need to be identified in a research project. This will help researchers in creating appropriate controls in research. There are numerous techniques to ensure that a study is internally valid. Still, there is also a list of potential risks to internal validity that need to be considered while designing a study. Consider the following typical threats:

Historical Events

Historical events have an impact on the outcomes of research conducted during a given time period. This is because many events might influence how people feel or respond to a certain subject. For example, changes in political leadership or natural disasters can have an impact on how survey respondents think and behave.


Experiments that are performed over a lengthy moment are most vulnerable to maturation. The effect of time as a variable in research is explained in this way. It may be difficult to prove that the results of your research were not affected by time if your subjects grew older or went through a biological change.

Experimenter bias

This happens when the experimenter behaves differently in one group than in another. This can be for or against the group. The researcher’s bias may have an impact on the study’s findings. If an experimenter behaves differently in different study groups, it may have an effect on the results and reduce the study’s internal validity.


This happens when experiment participants interact and observe one another, compromising the study’s findings’ reliability. Resentful demoralization is an issue that might arise as a result of this. Members of the control group here work less hard because they feel resentful of their group.


Experiments can require testing the same subjects multiple times in order to collect more accurate information. Testing participants with the same measurements on a regular basis has an impact on their results. Participants are likely to do better as they learn the test or become more familiar with the testing process; therefore, repeated testing could significantly impact outcomes.

Internal validity Examples

Internal validity can be seen in the following examples:

Example 1

Internal validity is lower in an inquiry that examines the link between income level and the risk of smoking. According to a study, there is a correlation between smoking and being a low-income person.

Occupation, culture, education, social standing, and other variables are examples of different sorts of factors. Such factors cannot be eliminated from the research. Internal validity is a concept that aids in establishing that you have evidence that your findings have a major impact on the outcomes.

Example 2

An investigator performs research to examine the effect of specially designed computer applications for teaching on traditional classroom techniques. According to the study’s findings, children who are taught using computer software learn faster.

Another finding of this research is that computerized teaching has significantly improved children’s grade levels. Other researchers’ research suggests that youngsters taught using computer software believe they are not being paid attention to.

Because research manipulation has an impact, an experiment still has great internal validity. The construct validity of the study report studies is low because the cause is not defined clearly. The researcher prioritizes attention over the benefits of computer programs.

Example 3

Internal validity requires correlation, which occurs when the two events occur at the same time. For example, the egg must directly result from the chicken’s biological abilities. The study must also be non-spurious, which indicates that no other believable possibility exists, such as an angel continuously impregnating all hens on the globe.

Example 4

Another example of internal validity is time priority or proving that the cause occurred before the consequence. One could argue that smoking cigarettes cause lung cancer by demonstrating that most of those treated had a smoking history.


An experiment cannot demonstrate a causal link between two variables unless it has strong internal validity. Internal validity ensures that the experiment design selected by the researcher complies with the concept of cause and effect. It lends credibility and trustworthiness to the conclusions of a causal link.

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