Internal and External Validity
Both internal and external validity are incredibly significant factors in a research study. If a research study is not valid there is no reason to rely on the information gathered. Internal validity is the extent that a researcher can trust the results of their research based on the relationship of the independent and dependent variable rather than external factors. Whereas, external validity refers to how much the results of a research study can be generalized.
There are many different ways both types of validities can affect research studies. For instance, when it comes to dealing with internal validity there is a threat to the validity when an endogenous change occurs. An endogenous change has a few different types in itself, maturation, testing, and regression. Maturation in this sense appears when an experiment happens over an extended amount of time. The people involved in the experiment change and grow with
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When it comes to external validity selection bias may be a threat. In external validity a researcher is trying to find a very generalized outcome that will apply to more than just the groups they are testing. If the subjects collected for the experiment are not randomly selected it opens up the threat of selection bias. For example, if a researcher designed an experiment to test the average IQ of a person but selected subjects from either a higher achieved or lower achieved group, the outcomes may not be representative of the entire population.
Another situation that can cause different outcomes for external validity is testing. While testing was also mentioned in the threats to internal validity, different testing situations threaten external validity. If a researcher administers a pre-test to the subjects the outcome may not be generalizable to the overall population who will not experience the