An experimenter is interested in the influence of taking a one-semester-long test preparation course on performance on the Scholastic Aptitude Test (SAT). She contacts high school students who have and who have not taken the course and compares their scores on the SAT exam. She finds that the students who have taken the course score significantly higher on the test. Which of the following represents the principal threat to the internal validity of this experiment?

Question

Quizplus · Accepted Answer

The principal threat to the internal validity in this scenario is selection. This is because the experimenter is comparing two groups of students (those who have taken the test preparation course and those who have not) without randomly assigning them to these groups. This non-random assignment means that there could be pre-existing differences between the groups that are responsible for the observed differences in SAT scores, rather than the test preparation course itself.

An Experimenter Is Interested in the Influence of Taking a One-Semester-Long