How to Design and Evaluate Research in Education, 5/e

Jack R. Fraenkel, San Francisco State University
Norman E. Wallen, San Francisco State University

Internal Validity

Essay Quiz


1		Briefly describe the difference between internal and external validity.



2		List four general techniques for controlling threats to internal validity.



3		Identify the obvious threats to internal validity in the following research scenario: A researcher conducted a study to determine if projecting visual illustrations onto a screen during science class would enhance students' understanding of scientific principals. The researcher chose two classes for the study: a biology class and a chemistry class. He told one class that they would get to see color illustrations projected onto a screen. He told the other class that they would be the "control" group so they would not get the illustrations. Since the chemistry classroom already was technologically equipped, the researcher chose the chemistry class as the one that would see the illustrations. At the end of the semester the researcher asked for volunteers from the two classes to take a test to help him see if the illustrations were effective. Most of the students in the chemistry class, and about half of the students in the biology class, volunteered to take the test.

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