Provide an example of a simple study and one possible threat to internal validity. Describe a way that the threat could be reduced.

Example: An academic librarian conducted a study to determine the effectiveness of a lesson in online searching techniques on variety and quality of citations. They gave the lesson to the students in English 101 Section 001 and compared the variety and quality of citations on a research paper with the students in Section 002 (who did not receive the lesson).

Possible threat: Selection (Students in the two sections may already differ in the searching abilities before the lessons.)

One way to reduce the threat: Compare the variety and quality of citations in a paper submitted before the lessons.