19: Threats to Internal Validity
Threats to Internal Validity
- Aside from unrecognized differences prior to the start of a study, other factors play can threaten internal validity
- Mortality
- If study drop out rates or the type of subjects who drop out are different between groups, the result could significantly skew the results
- Hawthorne Effect
- The mere fact that a person is being observed or is taking part in a study can affect his or her behavior. If the effect is different between groups, internal validity is again threatened
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- Mortality