I do an experiment like the following (there are numerous
adaptations):
Have one student put a blue X on one side of a piece of
paper, a red X on the opposite side, fold the paper twice,
and staple it in the center. See how many papers the student
can produce in 30 seconds. Add a second student and see
how many they can produce together in 30 seconds, etc.
When the experiment is finished, compute the average
contribution of the students together and the marginal
contribution (you might want to use a less intimidating name)
of each student.
The issue is to show that marginal contribution and average
contribution are not always the same and that what is important
when deciding whether to add another student or not is NOT the
average contribution, but the marginal contribution.
Once the students see that there is a distinction between average
and margin and that margin is more useful in making decisions
about changes, the teacher can point out that micro is a study of
human and firm behavior as seen through the eyes of "margins".
--------------------------------------------------------------
Anthony Davies, Ph.D.
Department of Applied Economics
Wesleyan College
Buckhannon, WV 26201
davies@wvwc.edu
304.473.8477 (voice)
304.473.8479 (fax)