After they had failed the writing exam that was required of all students before graduation, fifteen students were placed in a class in which they received additional tutoring. After completing this class, all fifteen students retook the exam earned higher scores. Their success was held up as an example that the class curriculum really works. What source of internal invalidity has not been considered?
A) History Effect
B) Noncomparable Groups
C) Contamination
D) Regression
E) Placebo Effect

Question

Quizplus · Accepted Answer

The source of internal invalidity that has not been considered is regression. This is because students who initially score very low (as these fifteen did) will naturally tend to have higher scores on the second test, regardless of whether or not they received additional tutoring. This is a statistical phenomenon known as regression to the mean. Therefore, it cannot be concluded that the improved scores were solely due to the effectiveness of the class curriculum.

After They Had Failed the Writing Exam That Was Required