Published on May 15, 2019 by Raimo Streefkerk. Revised on November 30, 2022. Internal and external validity are two ways of testing cause-and-effect relationships. 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. The validity of a study is largely determined by the experimental design. To ensure the validity of the tools or tests you use, you also have to consider measurement validity. Trade-off between internal and external validityBetter internal validity often comes at the expense of external validity (and vice versa). The type of study you choose reflects the priorities of your research. Trade-off example A solution to this trade-off is to conduct the research first in a controlled (artificial) environment to establish the existence of a causal relationship, followed by a field experiment to analyze if the results hold in the real world. Threats to internal validityThere are eight factors that can threaten the internal validity of your research. They are explained below using the following example: Research example
Threats to external validityThere are three main factors that might threaten the external validity of our study example. Threats to external validity
There are various other threats to external validity that can apply to different kinds of experiments. Frequently asked questions about internal and external validityWhat is experimental design? Experimental design means planning a set of procedures to investigate a relationship between variables. To design a controlled experiment, you need:
When designing the experiment, you decide:
Experimental design is essential to the internal and external validity of your experiment. Cite this Scribbr articleIf you want to cite this source, you can copy and paste the citation or click the “Cite this Scribbr article” button to automatically add the citation to our free Citation Generator.
Is this article helpful?You have already voted. Thanks :-) Your vote is saved :-) Processing your vote... What makes a study have good internal validity?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.
Which of the following is a technique to improve internal validity?Researchers use the technique of blinding in order to improve internal validity. Blinding is the technique of randomizing the variables to reduce bias in the researchers and subjects.
What increases internal validity?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 are examples of internal validity?Another example of internal validity is time priority or proving that the cause occurred before the consequence. One could argue that smoking cigarettes cause lung cancer by demonstrating that most of those treated had a smoking history.
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