Threats To Internal Validity – 9 Biggest Threats To Research Validity In 2020

There might be affiliate links on this page, which means we get a small commission of anything you buy. As an Amazon Associate we earn from qualifying purchases. Please do your own research before making any online purchase.

The results of any research study are only conclusive and meaningful when they can be interpreted explicitly and confidently.

If you’re a researcher, you need to know about the concept of internal validity which pertains to precision and rigor of your study design. To carry out sound research, you ought to eliminate all the possible threats to internal validity.

It is a common belief that a study’s outcomes are valid and decisive just because it is a scientific study. Alas! This is not always the case.

Oftentimes, many internal and external factors come into play amid any research plan to invalidate the findings. You can find a plethora of scientific studies that crumble under the weight of biased, unreliable, and contentious data.

Here a question arises: How can you gain confidence that the research you conducted is of value?

Despite being a researcher, many of us are unmindful of internal validity.

This article is indeed a mega treat for all of you as we’ll turn your attention to the realm of science. We’ll make you aware of the fact that how different variables pose threats to internal validity in cause-effect studies. Also, we’ll share with you the best strategies on how can you reduce threats to internal validity.

Read Also:

Let’s get you straight to the main point.

What Exactly Is Internal Validity?

Internal validity is a scientific concept that reflects whether or not the study results are convincing and trustworthy. It relates to how well a study is conducted.

Scientific research cannot predict with certitude that the desired independent variable caused a change in the dependent variable. Here comes the concept of internal validity that establishes an accurate relationship between the two variables.

Test validity is concerned with the test's intended focus
It Is Vital For The Tests To Be Valid

Internal validity refers to the extent or degree to which a study can be dismissed or alternate explanations can be made of the results obtained. Bear in mind, a study is said to be valid only if it depicts what it aimed to.

Thus, internal validity is the extent to which you can confidently state that no other variable but the one you’re studying caused the entire effect.

Internal Validity Example:

Let’s suppose you ran an experiment to see if a particular medication promoted weight loss or not. Here, the drug that is thought to bring about the change is the independent variable while the amount or percentage of weight reduced (that we wish to measure) is the dependent variable.

How can you be sure that weight loss was due to your administered drug?

If you can avoid potential traps that cause a disparity in your study by using good experimental practices such as random sampling and assignment of participants in groups, controlling confounding variables that might affect your data, your internal validity will be high.

High internal validity suggests a correct relationship between your chosen dependent and independent variables. If that’s the case, you can say that weight loss was the effect of the drug you had given to your selected participants.

A good scientist strives for high internal validity
Attributes Of A Good Researcher

Come let’s have a deeper look into the typical threats to internal validity that skew your study towards another direction to make the results inconclusive.

 9 Most Common Threats To Internal Validity

Influences or forces other than the independent variable that may act to explain the study results are known as threats to internal validity. Getting yourself acquainted with these threats will help guide you in choosing an appropriate research design.

This way you’ll be able to minimize the factors that pose threats to the integrity of internal validity within the confines of your available resources.

Those of you who wish to get the entire list of the factors affecting the effectiveness of the study right here, you’re lucky enough, your wish has come true.

Here you go!

Threats to internal validity make the results indecisive
9 Biggest Threats To Internal Validity

Let’s discuss the factors that jeopardize internal validity.

1. Historical Events

History refers to events that occur outside the concerns of any research study. The participants of the study population are often subjected to alteration because of the role of various environmental factors that tend to influence the subject’s overall performance.

In an ongoing experiment, the events in the weather, in the country, or in the subjects’ personal lives are one of the great threats to internal validity. Therefore, these events need to be addressed.

For instance, any natural disaster can have a substantial impact on the outcome of the undertaken studies

2. Maturation

Maturation is a threat internal to the subjects. It refers to the changes-either physical, developmental, emotional, or mental- which occur over time within the study participants.

Maturation deals with the time and with the effect that time has on the growth and behavior of the participants. Factors such as subject tiredness, impatience, boredom, etc. affect internal validity. Also, subjects growing older and stronger are influential in reducing the validity of the research.

In general terms, one can say that the longer the duration of the study, the greater will be the maturation threat.

3. Confounding

What happens when variables other than your independent variable become operative?

Confounding relates to a situation in which various other factors blend in with your independent variable to make the outcomes confusing and questionable.

Confounding variables threaten the validity of the study findings
Confounding Is A Major Issue In Research Validation

Due to confounding, changes in the dependent variable may be ascribed to other variables that operate to manipulate the results. Confounding variables tend to increase variance and introduce bias.

Thus, eliminating the confounding variables can help you in developing a close and accurate causal relationship.

The more the confidence you have in a conducted study, the more you’ll be able to rule out alternative explanations for your results.

Moreover, the less the chance there is for confounding, the higher will be the internal validity.

4. Attrition

Some studies are short, others are long and extensive. Not all subjects participate in the study until the end. Dropping out of subjects before the completion of a study is known as attrition.

For experimental designs involving more than one group, the loss of subjects leads to controversial inferences.

The reduction in the sample size due to any reason is one of the major threats to internal validity.

5. Testing

When you repeatedly test the participants for the same measures, it may lead to bias. Consequently, the individuals will do better in the next similar tests because of the prior information you have provided.

The participants will perform just based on the information conveyed to them via repeated testing. Such results may not be accurate.

Also, the pre-test before the program may give clues to the participants. Familiarity with the test is a threat to your experimental layout as it can overstate or understate your program’s motive.

6. Instrumentation

If you change the testing procedure or instrument, you are more likely to observe unwanted alterations in pre-tests and post-tests.

This is one of the chief reasons that we optimize the testing procedure and standardize the instrument before conducting valid research in any discipline.

7. Statistical Regression

In stats, regression analysis estimates the strength of the relationship between the variables under focus.

This threat is posed by the selection of subjects with extreme scores (far away from the mean) during a test. This means subjects that display extreme scores (outliers) tend to move towards the mean and natural distribution with repeated testing.

For example, when children with the worst reading scores are invited to take part in a related study, the improvements you may observe at the end of the course might be due to the regression towards the mean rather than the course efficacy.

This statistical regression threat undermines the objective and effectiveness of the overall study.

8. Diffusion

If the treatment effects begin to spread from the treatment group (experimental) to the control group (healthy) through the mutual interaction of the subjects falling in two different groups, the results will vary profoundly.

When the control group becomes contaminated by communication with the experimental group, the behavior of the control group toward the study may be considerably influenced. So, this very threat can diminish the differences that are to be seen in two different groups at two different levels. This makes your results ambiguous and indecisive.

This diffusion concern can lead to another issue called resentful demoralization. Participants in the control group become resentful of their assigned group.

Furthermore, demoralization is one of the great threats to internal validity as it may increase the dropout rates due to the popping up of negative feelings such as anger, frustration, resentment, etc. in the control subjects.

9. Experimenter Bias

Experimenter bias arises when the experimenter inadvertently affects the result by behaving differently or differentially with the members of experimental and control groups. In other words, this may be called unintended favoritism that can harm the participants of the two groups.

After learning about the main concerns’ and threats to internal validity, it’s high time we discuss the strategies you can use to improve internal validity. Evaporating these threats from your study plan will work out the best for achieving favorable results.

How To Reduce Threats To Internal Validity?

If you’re someone looking to improve the internal validity of your experiment, you’ll have to focus on your research design.

Here are some of the factors that can help reduce threats to internal validity which will ultimately make the results indisputable and unarguable.

Reducing threats to internal validity improve the overall validity of the study
4 Best Strategies On Improving Internal Validity

1.Random selection

Random selection relates to how samples are selected at random from the population for inclusion in the program. This gives each subject an equal chance to participate in the designed study.

2. Randomization/Random assignment

It is an aspect of research design in which you randomly allocate the participants to the treatment and control groups. This ensures no systematic bias exists between the study groups.

3. Blinding

Blinding or masking is a crucial method in which all persons– either the participants or the researchers or both- are unaware of the type of treatment or intervention that each participant receives.

It is also possible that the researcher is blinded to make sure that he/she doesn’t know which group is receiving what.

Blinding is implemented in a range of scientific study designs to eliminate conscious or unconscious experimenter bias.

4. Study protocols

Following strict and specific procedures for the administration of the treatment, help get results that are significant and trustworthy.

Therefore, standardizing the measurement methods and recruiting trained experimenters and observers can improve the consistency of the measurement techniques as well as lead to correct inferences.

FAQ – Frequently Asked Questions about Threats to Internal Validity

What are the controls for the threats to internal validity?

The threats talked about are choice mortality, history, development, testing, instrumentation, measurable relapse, communications with determination vagueness about the course of causal impact, dispersion of impersonation of medications, compensatory adjustment of medicines, and compensatory contention by respondents.

What factors affect internal validity?

History, Time given for the data collection, Size of the subject population, Subject variability, Attrition, task sensitivity and Maturation are the factors that affect the internal validity.

What increases internal validity?

At the point when you guarantee Internal Validity you are stating that in your research, you can dole out causes to impacts unambiguously. Randomization is a useful asset for expanding inner legitimacy. This is about the legitimacy of applying your investigation decisions outside, or outer too.

What is internal validity in psychology?

Internal validity alludes to whether the impacts saw in an examination are because of the control of the free factor and not some other factor.


For the benefit, we’d like to epitomize the article on threats to internal validity in a few lines.

Internal validity gives the researcher the credence that the conclusions he made reflect largely what he’s studying. It depends stringently on the study procedures and measures how rigorously the study is conducted.

There are several factors that lower the internal validity of a study. Threats to internal validity are primarily due to extraneous variances and influences that act to make the study results insignificant.

Controlling confounding variables, in particular, can help achieve the best of everything.

Those of you who long for conducting a scientific study, keeping all the above-mentioned threats in mind, you can reach the pinnacle of your career.

We’ll sum up with the famous quote of Francis Bacon:

“Man prefers to believe what he prefers to be true.”

Further Reading:

Leave a Comment