As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsem*nt of, or agreement with, the contents by NLM or the National Institutes of Health.
Learn more: PMC Disclaimer | PMC Copyright Notice
J Bras Pneumol. 2018 May-Jun; 44(3): 183.
CLINICAL SCENARIO
In a multicenter study in France, investigators conducted a randomized controlled trial to test the effect of prone vs. supine positioning ventilation on mortality among patients with early, severe ARDS. They showed that prolonged prone-positioning ventilation decreased 28-day mortality [hazard ratio (HR) = 0.39; 95% CI: 0.25-0.63].1
STUDY VALIDITY
The validity of a research study refers to how well the results among the study participants represent true findings among similar individuals outside the study. This concept of validity applies to all types of clinical studies, including those about prevalence, associations, interventions, and diagnosis. The validity of a research study includes two domains: internal and external validity.
Internal validity is defined as the extent to which the observed results represent the truth in the population we are studying and, thus, are not due to methodological errors. In our example, if the authors can support that the study has internal validity, they can conclude that prone positioning reduces mortality among patients with severe ARDS. The internal validity of a study can be threatened by many factors, including errors in measurement or in the selection of participants in the study, and researchers should think about and avoid these errors.
Once the internal validity of the study is established, the researcher can proceed to make a judgment regarding its external validity by asking whether the study results apply to similar patients in a different setting or not (Figure 1). In the example, we would want to evaluate if the results of the clinical trial apply to ARDS patients in other ICUs. If the patients have early, severe ARDS, probably yes, but the study results may not apply to patients with mild ARDS. External validity refers to the extent to which the results of a study are generalizable to patients in our daily practice, especially for the population that the sample is thought to represent.
Internal and external validity.
Lack of internal validity implies that the results of the study deviate from the truth, and, therefore, we cannot draw any conclusions; hence, if the results of a trial are not internally valid, external validity is irrelevant.2 Lack of external validity implies that the results of the trial may not apply to patients who differ from the study population and, consequently, could lead to low adoption of the treatment tested in the trial by other clinicians.
INCREASING VALIDITY OF RESEARCH STUDIES
To increase internal validity, investigators should ensure careful study planning and adequate quality control and implementation strategies-including adequate recruitment strategies, data collection, data analysis, and sample size. External validity can be increased by using broad inclusion criteria that result in a study population that more closely resembles real-life patients, and, in the case of clinical trials, by choosing interventions that are feasible to apply.2
REFERENCES
1. Guérin C, Reignier J, Richard JC, Beuret P, Gacouin A, Boulain T. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med. 2013;368(23):2159–2168. doi:10.1056/NEJMoa1214103. [PubMed] [CrossRef] [Google Scholar]
2. Akobeng AK. Assessing the validity of clinical trials. J Pediatr Gastroenterol Nutr. 2008;47(3):277–282. doi:10.1097/MPG.0b013e31816c749f. [PubMed] [CrossRef] [Google Scholar]
Articles from Jornal Brasileiro de Pneumologia are provided here courtesy of Sociedade Brasileira de Pneumologia e Tisiologia (Brazilian Thoracic Society)
FAQs
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.
What is internal and external validity in medical research? ›
Internal validity examines whether the study design, conduct, and analysis answer the research questions without bias. External validity examines whether the study findings can be generalized to other contexts.
How can a researcher balance between the internal and external validity? ›
To balance the trade-offs between internal and external validity in research design, it is important to define the research question and purpose clearly, and align them with the research design and methods.
What is the internal and external validity of results in experimental research? ›
Internal validity is the degree of confidence that the causal relationship you are testing is not influenced by other factors or variables. External validity is the extent to which your results can be generalized to other contexts. The validity of your experiment depends on your experimental design.
How to maximize internal and external validity? ›
INCREASING VALIDITY OF RESEARCH STUDIES
To increase internal validity, investigators should ensure careful study planning and adequate quality control and implementation strategies-including adequate recruitment strategies, data collection, data analysis, and sample size.
What is the trade off between internal and external validity? ›
The tradeoff is reframed as a tradeoff between the degree of confidence that a researcher can attain about the internal validity of her result and the degree of confidence she can attain regarding its external validity. This interpretation of the tradeoff is compatible with the prerequisite view.
What is internal and external evidence in healthcare? ›
External evidence includes systematic reviews, randomized control trials, best practice, and clinical practice guidelines that support a change in clinical practice. Internal evidence includes health care institution based quality improvement projects, outcome management initiatives, and clinical expertise.
How well do a researcher's findings apply to other individuals and situations? ›
External validity is how relatable and applicable research findings are to other situations and the real world. This is important because research aims to provide knowledge about the real world.
What are examples of internal validity research? ›
Internal validity examples
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.
What is the correlation between internal validity and external validity? ›
Internal validity relates to how well a study is conducted (its experimental design and methods), while external validity relates to how applicable and generalizable the findings are to the world at large.
Failure to do the appropriate planning for both internal and external validity can cause your experiment or study to produce results that you cannot trust! Various types of bias can reduce both internal and external validity. These include Selection Bias, Sampling Bias, and Cognitive Bias.
Why do internal and external validity conflict? ›
There are several conflicts within internal and external validity. Researchers who want more internal validity are likely to do their study in a more rigorous, controlled setting which allows for high internal validity but a low external validity. This would be applicable to external validity as well.
What is the internal and external validity of research design? ›
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 is internal and external reliability in research? ›
Internal reliability- Internal reliability assesses the consistency of results across items within a test. External reliability- External reliability refers to the extent to which a measure varies from one use to another.
Is internal or external validity more important? ›
It has been frequently argued that internal validity is the priority for research. 4 However, in an applied discipline, the purpose of which includes working to improve the health of the public, it is also important that external validity be emphasized and strengthened.
Does qualitative research have internal and external validity? ›
In a similar fashion to transferability serving in place of external validity, qualitative research discusses the credibility of the findings to understand a study's internal validity. In qualitative research, credibility refers to the confidence that the data and its analysis are valid and reliable.
Can a study have strong internal validity and weak external validity? ›
A study can have a strong internal validity but weak external validity at the population level.
What is a concurrent validity example? ›
Concurrent validity is a term used to denote assessments that give similar results when used in a short time frame. For example, a therapist may use two separate depression scales with a patient to confirm a diagnosis. As long as both the assessments give the same results, they are concurrently valid.
