Threats to External Validity

An experiment is said to have external validity when its results can be generalized to other settings (ecological validity), other people (population validity), and over time. The external validity can be affected by multiple factors. Interactions: Between Testing and Treatment: When a pre-test exposes the individual to the purpose of the test and, in turn, […]

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Threats to Internal Validity

Internal validity is threatened when the experiment cannot maximize the effects of independent variable, cannot control the effects of extraneous variable(s), and/or cannot minimize the effects of random error(s). History: when an unanticipated event occurs during the experiment and influences the dependent variable. This is something in the environment (e.g. change in weather). It can […]

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Validity

Validity of a study explains how much of the change in the dependent variable was due to the independent variable. If validity is high, most of the change was due to the independent variable. In testing, a test is considered to have high validity if it measures what it’s supposed to measure. In statistics, validity can […]

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