Table of ContentsView AllTable of ContentsInternal ValidityExternal ValidityComparisonExamples

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Internal Validity

External Validity

Comparison

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How do you determine whether a psychology study is trustworthy and meaningful? Two characteristics that can help you assess research findings are internal and external validity.

These two concepts help researchers gauge if the results of aresearch studyare trustworthy and meaningful.

Internal ValidityConclusions are warrantedControls extraneous variablesEliminates alternative explanationsFocus on accuracy and strong research methodsExternal ValidityFindings can be generalizedOutcomes apply to practical situationsResults apply to the world at largeResults can be translated into another context

Internal ValidityConclusions are warrantedControls extraneous variablesEliminates alternative explanationsFocus on accuracy and strong research methods

Conclusions are warranted

Controls extraneous variables

Eliminates alternative explanations

Focus on accuracy and strong research methods

External ValidityFindings can be generalizedOutcomes apply to practical situationsResults apply to the world at largeResults can be translated into another context

Findings can be generalized

Outcomes apply to practical situations

Results apply to the world at large

Results can be translated into another context

What Is Internal Validity in Research?

Internal validity is the extent to which a research study establishes a trustworthy cause-and-effect relationship.This type of validity depends largely on the study’s procedures and how rigorously it is performed.

Internal validity is important because once established, it makes it possible to eliminate alternative explanations for a finding. If you implement a smoking cessation program, for instance, internal validity ensures that any improvement in the subjects is due to the treatment administered and not something else.

Internal validity is not a “yes or no” concept. Instead, we consider how confident we can be with study findings based on whether the research avoids traps that may make those findings questionable. The less chance there is for “confounding,” the higher the internal validity and the more confident we can be.

Confounding refers to uncontrollablevariablesthat come into play and can confuse the outcome of a study, making us unsure of whether we can trust that we have identified the cause-and-effect relationship.

In short, you can only be confident that a study is internally valid if you can rule out alternative explanations for the findings. Three criteria are required to assume cause and effect in a research study:

Factors That Improve Internal Validity

To ensure the internal validity of a study, you want to consider aspects of the research design that will increase the likelihood that you can reject alternative hypotheses. Many factors can improve internal validity in research, including:

Internal Validity Threats

Just as there are many ways to ensure internal validity, a list of potential threats should be considered when planning a study.

What Is External Validity in Research?

External validity refers to how well the outcome of a research study can be expected to apply to other settings. This is important because, if external validity is established, it means that the findings can be generalizable to similar individuals or populations.

External validity affirmatively answers the question: Do the findings apply to similar people, settings, situations, and time periods?

Population validity and ecological validity are two types of external validity. Population validity refers to whether you can generalize the research outcomes to other populations or groups. Ecological validity refers to whether a study’s findings can be generalized to additional situations or settings.

Another term called transferability refers to whether results transfer to situations with similar characteristics. Transferability relates to external validity and refers toa qualitative researchdesign.

Factors That Improve External Validity

If you want to improve the external validity of your study, there are many ways to achieve this goal. Factors that can enhance external validity include:

External Validity Threats

External validity is threatened when a study does not take into account the interaction of variables in the real world.Threats to external validity include:

Internal Validity vs. External Validity

Internal validity and external validity are two research concepts that share a few similarities while also having several differences.

Similarities

One of the similarities between internal validity and external validity is that both factors should be considered when designing a study. This is because both have implications in terms of whether the results of a study have meaning.

Both internal validity and external validity are not “either/or” concepts. Therefore, you always need to decide to what degree a study performs in terms of each type of validity.

Each of these concepts is also typically reported in research articles published inscholarly journals. This is so that other researchers can evaluate the study and make decisions about whether the results are useful and valid.

Differences

The essential difference between internal validity and external validity is that internal validity refers to the structure of a study (and its variables) while external validity refers to the universality of the results. But there are further differences between the two as well.

For instance, internal validity focuses on showing a difference that is due to the independent variable alone. Conversely, external validity results can be translated to the world at large.

Internal validity and external validity aren’t mutually exclusive. You can have a study with good internal validity but be overall irrelevant to the real world. You could also conduct a field study that is highly relevant to the real world but doesn’t have trustworthy results in terms of knowing what variables caused the outcomes.

Examples of Validity

Perhaps the best way to understand internal validity and external validity is with examples.

Internal Validity Example

An example of a study with good internal validity would be if a researcher hypothesizes that using a particularmindfulnessapp will reduce negative mood. To test this hypothesis, the researcher randomly assigns a sample of participants to one of two groups: those who will use the app over a defined period and those who engage in a control task.

A strict study protocol is also used to outline the procedures of the study. Potentialconfounding variablesare measured along withmood, such as the participants' socioeconomic status, gender, age, and other factors. If participants drop out of the study, their characteristics are examined to make sure there is no systematic bias in terms of who stays in.

External Validity Example

An example of a study with good external validity would be if, in the above example, the participants used the mindfulness app at home rather than in the laboratory. This shows that results appear in a real-world setting.

To further ensure external validity, the researcher clearly defines the population of interest and chooses arepresentative sample. They might also replicate the study’s results using different technological devices.

Takeaways

Setting up an experimentso that it has both sound internal validity and external validity involves being mindful from the start about factors that can influence each aspect of your research.

It’s best to spend extra time designing a structurally sound study that has far-reaching implications rather than to quickly rush through the design phase only to discover problems later on. Only when both internal validity and external validity are high can strong conclusions be made about your results.

An Overview of the Scientific Method

11 SourcesVerywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Andrade C.Internal, external, and ecological validity in research design, conduct, and evaluation.Indian J Psychol Med. 2018;40(5):498-499. doi:10.4103/IJPSYM.IJPSYM_334_18San Jose State University.Internal and external validity.Kemper CJ.Internal validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-3. doi:10.1007/978-3-319-28099-8_1316-1Patino CM, Ferreira JC.Internal and external validity: can you apply research study results to your patients?J Bras Pneumol. 2018;44(3):183. doi:10.1590/S1806-37562018000000164Matthay EC, Glymour MM.A graphical catalog of threats to validity: Linking social science with epidemiology.Epidemiology. 2020;31(3):376-384. doi:10.1097/EDE.0000000000001161Amico KR.Percent total attrition: a poor metric for study rigor in hosted intervention designs.Am J Public Health. 2009;99(9):1567-1575. doi:10.2105/AJPH.2008.134767Kemper CJ.External validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-4. doi:10.1007/978-3-319-28099-8_1303-1Desjardins E, Kurtz J, Kranke N, Lindeza A, Richter SH.Beyond standardization: improving external validity and reproducibility in experimental evolution. BioScience. 2021;71(5):543-552. doi:10.1093/biosci/biab008Drude NI, Martinez Gamboa L, Danziger M, Dirnagl U, Toelch U.Improving preclinical studies through replications.Elife. 2021;10:e62101. doi:10.7554/eLife.62101Michael RS.Threats to internal & external validity: Y520 strategies for educational inquiry.Pahus L, Burgel PR, Roche N, Paillasseur JL, Chanez P.Randomized controlled trials of pharmacological treatments to prevent COPD exacerbations: applicability to real-life patients.BMC Pulm Med. 2019;19(1):127. doi:10.1186/s12890-019-0882-y

11 Sources

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Andrade C.Internal, external, and ecological validity in research design, conduct, and evaluation.Indian J Psychol Med. 2018;40(5):498-499. doi:10.4103/IJPSYM.IJPSYM_334_18San Jose State University.Internal and external validity.Kemper CJ.Internal validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-3. doi:10.1007/978-3-319-28099-8_1316-1Patino CM, Ferreira JC.Internal and external validity: can you apply research study results to your patients?J Bras Pneumol. 2018;44(3):183. doi:10.1590/S1806-37562018000000164Matthay EC, Glymour MM.A graphical catalog of threats to validity: Linking social science with epidemiology.Epidemiology. 2020;31(3):376-384. doi:10.1097/EDE.0000000000001161Amico KR.Percent total attrition: a poor metric for study rigor in hosted intervention designs.Am J Public Health. 2009;99(9):1567-1575. doi:10.2105/AJPH.2008.134767Kemper CJ.External validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-4. doi:10.1007/978-3-319-28099-8_1303-1Desjardins E, Kurtz J, Kranke N, Lindeza A, Richter SH.Beyond standardization: improving external validity and reproducibility in experimental evolution. BioScience. 2021;71(5):543-552. doi:10.1093/biosci/biab008Drude NI, Martinez Gamboa L, Danziger M, Dirnagl U, Toelch U.Improving preclinical studies through replications.Elife. 2021;10:e62101. doi:10.7554/eLife.62101Michael RS.Threats to internal & external validity: Y520 strategies for educational inquiry.Pahus L, Burgel PR, Roche N, Paillasseur JL, Chanez P.Randomized controlled trials of pharmacological treatments to prevent COPD exacerbations: applicability to real-life patients.BMC Pulm Med. 2019;19(1):127. doi:10.1186/s12890-019-0882-y

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Andrade C.Internal, external, and ecological validity in research design, conduct, and evaluation.Indian J Psychol Med. 2018;40(5):498-499. doi:10.4103/IJPSYM.IJPSYM_334_18San Jose State University.Internal and external validity.Kemper CJ.Internal validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-3. doi:10.1007/978-3-319-28099-8_1316-1Patino CM, Ferreira JC.Internal and external validity: can you apply research study results to your patients?J Bras Pneumol. 2018;44(3):183. doi:10.1590/S1806-37562018000000164Matthay EC, Glymour MM.A graphical catalog of threats to validity: Linking social science with epidemiology.Epidemiology. 2020;31(3):376-384. doi:10.1097/EDE.0000000000001161Amico KR.Percent total attrition: a poor metric for study rigor in hosted intervention designs.Am J Public Health. 2009;99(9):1567-1575. doi:10.2105/AJPH.2008.134767Kemper CJ.External validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-4. doi:10.1007/978-3-319-28099-8_1303-1Desjardins E, Kurtz J, Kranke N, Lindeza A, Richter SH.Beyond standardization: improving external validity and reproducibility in experimental evolution. BioScience. 2021;71(5):543-552. doi:10.1093/biosci/biab008Drude NI, Martinez Gamboa L, Danziger M, Dirnagl U, Toelch U.Improving preclinical studies through replications.Elife. 2021;10:e62101. doi:10.7554/eLife.62101Michael RS.Threats to internal & external validity: Y520 strategies for educational inquiry.Pahus L, Burgel PR, Roche N, Paillasseur JL, Chanez P.Randomized controlled trials of pharmacological treatments to prevent COPD exacerbations: applicability to real-life patients.BMC Pulm Med. 2019;19(1):127. doi:10.1186/s12890-019-0882-y

Andrade C.Internal, external, and ecological validity in research design, conduct, and evaluation.Indian J Psychol Med. 2018;40(5):498-499. doi:10.4103/IJPSYM.IJPSYM_334_18

San Jose State University.Internal and external validity.

Kemper CJ.Internal validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-3. doi:10.1007/978-3-319-28099-8_1316-1

Patino CM, Ferreira JC.Internal and external validity: can you apply research study results to your patients?J Bras Pneumol. 2018;44(3):183. doi:10.1590/S1806-37562018000000164

Matthay EC, Glymour MM.A graphical catalog of threats to validity: Linking social science with epidemiology.Epidemiology. 2020;31(3):376-384. doi:10.1097/EDE.0000000000001161

Amico KR.Percent total attrition: a poor metric for study rigor in hosted intervention designs.Am J Public Health. 2009;99(9):1567-1575. doi:10.2105/AJPH.2008.134767

Kemper CJ.External validity. In: Zeigler-Hill V, Shackelford TK, eds.Encyclopedia of Personality and Individual Differences. Springer International Publishing; 2017:1-4. doi:10.1007/978-3-319-28099-8_1303-1

Desjardins E, Kurtz J, Kranke N, Lindeza A, Richter SH.Beyond standardization: improving external validity and reproducibility in experimental evolution. BioScience. 2021;71(5):543-552. doi:10.1093/biosci/biab008

Drude NI, Martinez Gamboa L, Danziger M, Dirnagl U, Toelch U.Improving preclinical studies through replications.Elife. 2021;10:e62101. doi:10.7554/eLife.62101

Michael RS.Threats to internal & external validity: Y520 strategies for educational inquiry.

Pahus L, Burgel PR, Roche N, Paillasseur JL, Chanez P.Randomized controlled trials of pharmacological treatments to prevent COPD exacerbations: applicability to real-life patients.BMC Pulm Med. 2019;19(1):127. doi:10.1186/s12890-019-0882-y

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