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Increasing Internal Validity can decrease External Validity

A good experiment has to have Internal and External validity. Checking for validity is like answering a question of whether the experiment has been designed well, whether the variables that are being measured are really affected by variables that are being manipulated in this particular experiment or if they are affected by something else.
Checking for Internal Validity determines whether "the connection between the independent variable and dependent variable clear and unambiguous to make a causal inference? (Leman, 1991). It's making sure that all the confounding factors are eliminated for the experiment.
External Validity has to do with the results. An experiment that has external validity will be able to have results that can be generalized across population at large.

Question to be answered:

Discuss why increasing one type decreases the other type.

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Increasing Internal Validity can decrease External Validity and vice versa. Why?
Having more control over the experiment (the environment, etc.) increases internal validity. The more confounding factors can be eliminated from the ...

Solution Summary

Validity effects are noted.