Internal Validity (An Update)

External and internal validity reflects on the validation of a study taken up and whether the results proposed by that study are meaningful and trustworthy or not.

While internal validity works on validation of the structure and working of the study, external validation works on validating the study applications in the real world and whether it is beneficial or not.

In this article, we will discuss internal validity in detail.

Internal Validity

Internal validity is basically to evaluate whether the proposed study establishes a good and trustworthy relationship between the treatment and outcome.

This also explains if a given study covers all possible outcomes and eliminates any other possible alternatives for a finding.

For example, if there is a smoking cessation program going on and you have administered them with some treatment, how can one be sure that the improvement shown by the group after treatment is because of the medicines or therapy or treatment implemented by you ?

The main purpose of the internal validity is to check on the procedures of study and how well it has been carried out.

Internal validity is not a concept with a definite “yes or no” outcome.

Insteadt, it is more of how confident the study is with the findings declared in the study and whether that study avoids the traps that can make those findings void.

Internal validity can be higher if the chances of a “confounding” element in the study is less, confounding refers to such a scenario where multiple factors come into play to make the findings in that study more confusing or questionable. 

In short, a study can only be declared as internally valid if every other alternative explanations for the specific findings have already been ruled out.

You can assume that your study meets the criteria for cause-and-effect once it meets the following three requirements: 

  1. The cause mentioned in the study always precedes the effect in terms of time.
  2. The cause and effect vary together.
  3. There are no other explanations of the relationship observed in the study.

Factors That Improve Internal Validity

If you want to increase the internal validity of the study you are carrying out, you need to work on the research design for that study and make it such that it automatically rejects any other hypothesis for that study.

There are multiple factors which can be considered to improve internal validity.

  • Randomization refers to the process of assigning participants to control and treatment groups randomly, and making sure that there is no systematic bias between those groups.
  • Random selection refers to the selection of participants randomly from the group of representatives that the study is focused on.
  • Blinding refers to not giving full information to participants about the intervention or study they are partaking in, sometimes it even is applicable on researchers, this help them to remain unbiased during the time of study and not develop biased perceptions before the study is carried out.
  • Experimental manipulation refers to the manipulation of an independent variable during the course of study instead of just observing the under study group, later interventions can be introduced with the group and observations can be done of its impact. 
  • Study protocol refers to doing the study according to some specific set of rules and procedures to administer the treatment to the selected group of people so as to there is no such difference in the criteria carried out for treatment for the same study in different groups.

Factors That Threaten Internal Validity

Just as we have seen that there are multiple ways to ensure the study taken out is internally valid, there are also some factors or potential threats which should be considered when researching the internal validity of one’s study.

  • Confounding refers to a certain scenario where changes that occur in a study might be considered because of the involvement of a third variable and not entirely because of the treatment that you are implementing on that group.
  • Historical events may also be influential towards the outcome of a study that may take some period of time. Some examples of such events are natural disasters or changes in political power of the country can influence how the participants act and feel during the study. 
  • Maturation refers to the impact that may be caused due to the change in participant behaviour because of age or some natural phenomena during the time of  the study. It can be caused because of a number of different factors, the participant might be growing older during the study period, or tired during some part of the study.
  • Testing refers when the participants involved in the study are tested according to the same measures repeatedly. 
  • Instrumentation refers to the actual instruments used and their impact for testing the response of the participants in the study. It is possible to “prime” the participants in a study in different ways, one can be the use of instruments which might result in the participants responding in a completely different way then they normally would to some task in a study.
  • Statistical regression refers for the participants that are at the extreme measures of a certain measure going into a certain direction because of the natural effect in due passage of time rather than going in that direction because of the intervention that you administered. 
  • Attrition refers to those participants that leave the study in between or drop out due to some reason and the results are then biased towards the participants in the study who have not left who might have something in common.
  • Diffusion refers to collecting both the control and the treatment group together using talking and group discussions or just observations. This might lead to another issue in the control group known as resentful demoralization as they are resentful towards the other group and try less hard for the interaction.

External Validity

External validity is the measure of how well the outcome of a study will be once it is applied to different settings.

This type of validity is a measure of how generalized the findings are and are they applicable on different studies with the same outcome.

Ecological validity is another form of external validity, that looks at the real aspects of the study to check if the proposed study and its findings can be applied to real world scenarios.

While there may be multiple methods to make sure the internal validity of a study remains intact, the external validity of a study is dependent on limited methods as explained below.

Factors that Improve External Validity

What can be done to improve the external validity ?

  • Inclusion and exclusion criteria:  This defines that the population used for the study in your research has been clearly defined.
  • Psychological realism refers that the participants in the study are taking the experiment as a real life experience event which can be made sure by informing them of a cover story related to the study and its aim. Otherwise, in most cases the participants might not take the study seriously and will not respond to it as they might have done it in their real life.
  • Replication refers to the conduction of the same study with different samples or in different settings to check whether the results are the same or not. 
  • Field experiments can also be considered when conducting a study as sometimes the study can be carried out in a natural setting rather than in the laboratory.
  • Reprocessing or calibration refers to the use of statistical methods to adjust the problems that might occur for an external validity like uneven groups based on some characteristics for the study. 

Factors That Threaten External Validity

There are also some factors that might be taken into account when designing the study for external validity as it might harm the chances for your study to be externally validated: 

  • Situational factors such as location, time of day, researcher characteristics, noise and number of measures used may affect the generalizability of findings.
  • Pre- and post-test effects refer to a certain scenario where the pre- or post-test of the study is in one way or another related to the effects seen due to treatment administered during the study such that without considering that test the cause-and-effect relationship in the study will disappear.
  • Sample features refer to the scenario where the results or end effects are dependent on a certain feature of a specific sample which might lead to limiting generalization of the findings.
  • Selection bias refers to the problems that might be present within different groups because of differences and might relate to an independent variable

Similarities and Differences of Internal and external validity

Internal and external validity might focus on different things in the research but they are basically different faces of a coin.

A research should have both internal and external validity in the balance, as a research with no application to the real world is not much important and in the same way a research that is carried out in context for the real world but the resources used are not reliable is not going to help out. 

Similarities of Internal and External Validity

What are the similarities between external and internal validity?

Internal and external validity are the factors that are considered whenever a research or study is being designed, both of these factors define the meaning of a study and its impact.

Both of them are not “either/or ” concepts that if one is valid the other is valid or if you are considering one validity, you cannot consider the other one.

They are standards to which a research group should decide where their research should perform in that standard’s scale.

Differences in Internal and External validity

The main difference between external and internal validity is the aspect of study they are focused on. Internal validity is more focused on the structure of a study and how well it is carried out whereas external validity focuses more on the results of the research and if they are applicable in real life scenarios. 

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Internal Validity

  • Focus on accuracy and strong research methods
  • Controls extraneous variables
  • Conclusions are warranted
  • Eliminates alternative explanations

External Validity

  • Results translate to world at large
  • Findings are generalizable
  • Outcomes apply to practical situations
  • Results can be translated into another context

FAQ about Internal Validity

What is internal validity in a research study?

Internal validity is a way to see if the resources used in the study and the way the study was carried out is done in a right way or not.

It also takes into measure if the problem observed or identified in the study can be taken into account considering any other hypothesis or not and calculates the validity for the study based on different variables. 

What are internal and external validity?

Internal validity refers to the degree of confidence that the causal relationship being tested is trustworthy and not influenced by other factors or variables.

External validity refers to the extent to which results from a study can be applied (generalized) to other situations, groups or events.

What are the threats to internal validity?

In total there are eight threads that are : instrumentation, maturation, experimental mortality, testing, regression, selection, history, and an interaction of threats.


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