If you want to have a little fun, tell the students that the
vice-president for green M&M's called you up in the middle of the night to
tell you that he wanted you to prove what he already knew: That consuming green
M&M's improves memory.
Have students design a simple experiment to test this hypothesis.
This demonstration gives you an opportunity to
1. Stress that they shouldn't use an empty control group because of the placebo effect
2. Re-emphasize what null results do and do not mean.
3. Stimulates discussion about what steps to use to maximize power.
4. Stress the value of double-blind procedures.
5. Introduce wrinkles that would improve external validity.
6. Stress the value of independent random assignment.
7. Demonstrate that the simple experiment is better than the simple pretest-posttest design because:
a. If the pretest/posttest design used the same memory test both times, the improved performance on the posttest could be due to practice effects (having studied the list twice rather than just once).
b. If different lists were used, we would expect poorer performance on the second list due to proactive interference. Furthermore, we would wonder if both lists were equally easy to remember.
8. Review the terminology of the simple experiment.
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