Question

Imagine in Dr. Paddock’s study that only 90 of the original participants completed the measure of homesickness during Week 7 (10 participants had left the university and were unavailable). What kind of threat to internal validity does this pose? How does this affect her conclusion that her treatment for homesickness worked?

Answer 1

With reference to previously posted Dr. Paddock problem, we understand their is necessity of internal validity due to the basis of the experiment being cause-and-effect relationships. Since this is a one-group design, history (occurance of unanticipated event while the experiment was in progress and these events changing the dependent variable) is the defined threat to the problem. Wikipedia also refers to this threat as Confounding.

This changes the statistics in her conclusion, but this can be rectified by handling the 90 participants exceptionally, and removing the 10 participants from the previous scoreboard.