Internal Validity Tutorial
http://psych.athabascau.ca/html/Validity/

This two-part tutorial offers activities for students to identify examples of threats to internal validity.

• Examine Part 1 of the tutorial to learn about nine sources of threats to internal validity. Then read the examples and associated explanations of why it does or does not represent a threat to internal validity.
• Participate in Part 2 of this tutorial, and classify 36 hypothetical experiments as internally valid or not. If not, select the threat to internal validity from one of the nine sources introduced in Part 1.
• What did you learn from this online activity? Which sources of threat do you think are most difficult to avoid? Least difficult to avoid? Why do you think so?