As a Secondary Mathematics Teacher, Hernandez Conducted a Study That

Multiple Choice

As a secondary mathematics teacher, Hernandez conducted a study that explored whether giving children recess prior to testing helped their test performance. For one of the semesters, he sends half of his classes out for 10 minutes of recess prior to testing for the other half, he provides 10 minutes of free time after the test.
-That Hernandez is the experimenter and the teacher administering the conditions, introduces which potential threat to validity?

A) Experimenter
B) Placebo
C) John Henry
D) Instrumentation