Internal vs. External Validity – Definition & Examples

12.12.22 Types of validity Time to read: 4min

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Internal and external validity are two fundamental measures in the methodology used in research to assess the quality and applicability of the results. Internal validity relates to the robustness of the research design and the extent to which it can provide evidence of a cause-and-effect relationship between variables. External validity concerns the generalizability of the findings to other contexts. Balancing them is a critical aspect of interpreting empirical research.

Internal vs. External Validity – In a Nutshell

The following can be said regarding internal vs. external validity based on the above article:

  •  The marginal distinction between internal vs. external validity is that internal validity can be managed; however, external validity depends on the study’s naturalness.
  • Generally, experimental research designs have internal vs. external validity.
  • Both internal vs. external validity play a significant role in research. Without internal vs. external validity, research is devoid of significance.

Definition: Internal vs. external validity

When examining cause-and-effect interactions, validity can be divided into internal vs. external validity.

Internal validity is the degree of assurance that the causal link being examined is reliable and unaffected by other variables and factors.

External validity is the extent to which the findings of a study may be extended to other contexts, groups, or events.

Experimental design affects study validity. Verify the measurement validity of your instruments or tests.

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Internal vs. external validity: A cooperation

External validity is frequently sacrificed for greater internal validity, and vice versa. The sort of study you select reflects the research’s priorities.

Discussed below is a trade-off between internal vs. external validity:


A causal relationship can be studied in a lab or “real world.” In a lab, external effects can be eliminated, boosting internal validity. External validity is weakened because a lab environment is different from “real world”. This trade-off can be resolved by researching in a controlled environment to verify a causal relationship, followed by a field experiment to test the conclusions in the real world.

Discussed below are the threats to internal vs. external validity:

Threats to internal validity

Eight factors can compromise your research’s internal validity. Several are explained using the following illustration:


The management of firm X wants to determine whether flexible work hours will increase employee job satisfaction. They designed an experiment involving two groups:

  1. Staff with fixed work hours as a control
  2. Test group with employees who have flexible work hours.

The duration of the experiment is six months. All employees complete a job satisfaction survey before (pre-test) and after(post-test) the experiment.

Threat Meaning Example
History Unanticipated occurrences alter the study's conditions and affect its outcome.
During the study, a new manager is hired, which boosts employee satisfaction.
Maturation The dependent variable is influenced by time.
Throughout the six-month experiment, people gained experience and became better at their professions. Consequently, job satisfaction could increase.
The pre-test influences the post-test findings.
Employees feel compelled to maintain consistency between their pre- and post-test responses.
Regression towards mean
On a second measurement,
extreme results approach the mean.
Employees who scored extremely low in the initial job satisfaction survey are likely to have a higher increase in job satisfaction than those who scored average.
Instrumentation During the study,
the dependent variable is measured differently.
The post-test questionnaire comprises additional questions compared to the pre-test questionnaire.

Social interaction
Interactions between individuals from distinct groups affect the outcome.
The group with fixed working hours resents the one with flexible working hours, and as a result, their job happiness declines.

Threats to external validity

To design a robust study, it is essential to identify and mitigate threats to external validity.


A researcher plans a two-month trial to see if regular mindfulness meditation helps persons with mental illness. They look for depressed people between 20 and 29 who reside nearby.

Participants are given a pre and post-test to measure the frequency with which they experienced anxiety throughout the past week. Each participant receives tailored mindfulness instruction and must practice every morning for 15 minutes.

The researcher concludes that mindfulness can assist all clinical populations because anxiety levels dropped between the pre and post-test results.

Threat Meaning Example
Sampling bias The sample does not adequately represent the population. The sample comprises depressed individuals. They possess traits that distinguish them from other clinical populations, such as those with personality disorders or schizophrenia
History An unconnected occurrence alters the results. A natural disaster strikes a neighboring state just before the pre-test.
Consequently, pre-test anxiety scores are more significant than they would be otherwise.
Experimenter effect Unintentionally, the qualities or actions of the experimenter influence the results. The mindfulness training instructor unintentionally emphasized the significance of this study for the research department's financing.
As a result, participants exert additional effort to minimize their anxiety throughout the study.
Hawthorne effect Participants' propensity to alter their behavior when they know they are being monitored. Participants actively avoid anxiety-provoking circumstances throughout the study since they know they are participating in research.
Testing effect Pre- or post-test administration influences the outcomes. Participants have less anxiety during the post-test because they are more familiar with the format and questions from the pre-test.
Situation effect The generalizability of the findings is hindered by variables such as the setting, time of day, geography, or researchers' characteristics. The study is replicated with one modification: the individuals now practice mindfulness in the evening.
This time, no progress is evident in the results.

Internal vs. external validity: Examples

Below are internal vs. external validity examples:


Internal validity:

  • You want to test if coffee boosts memory.
  • College-aged participants are randomized to morning and evening lab sessions. The morning session is the treatment group and the evening session is the control group.
  • The treatment group received coffee upon arriving at the lab, while the control group received water.
  • You also give memory tests to both groups.
  • After evaluating the results, it’s decided that the treatment group did better on the memory test than the control group.


External validity:

  • Memory test external validity is affected by participant inclusion criteria and lab conditions.
  • If you examine college-aged people, your results may only apply to them.
  • This improves internal validity and reduces external validity.
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Internal vs. external validity measures how accurately the independent variable affects the dependent variable. External validity generalizes research.

Internal vs. external validity focuses on extraneous variable control, while external validity emphasizes practical applicability.

Using a cognitive map, researchers may methodically address internal vs. external validity to reflect treatment effects and generalize findings appropriately.