Evaluate the threats to internal validity in the following scenario.

Researchers studied the relationship of counselors' moral reasoning to their level of empathy. Twenty-two counselors agreed to participate in the study. Each was administered Kohlberg's test for moral reasoning. Permission was obtained from some of the counselors' clients to have videotapes made of their counseling sessions. After watching the videotapes, experts gave each counselor an empathy rating. The correlation was then calculated between the score on the test of moral reasoning and the empathy rating.