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# Habits

This web page is part of a very small collection of essays on concepts related to the scientific method and to specific laboratory studies.

The following conversation actually took place in my laboratory classroom at Rice University.  Honest!

[student]  "My concentration for sample three is 3.1 mg/ml.  Is that right?"

[instructor]  "That's awfully low.  Did you consider the dilution factor?"

"Huh?"

"Did you conduct the assay on the sample after diluting it with water?"

"Oh...yes."

"So, by what factor did you dilute your sample?"

"Huh?"

"What volumes of sample and water did you mix?"

"Oh. We took 100 microliters of sample and added 900 microliters of water."

"Okay, so you have a ten-fold dilution factor.  Then all you have to do is multiply your concentration by ten."

"Oooooo.  Do you have a calculator?"

I do hope that your reaction is some combination of amusement, incredulity, frustration, and/or empathy (if you are a teacher, that is).  If you don't "get" it, then you are probably offended by this anecdote.

The story illustrates a common problem in undergraduate education, that is, compartmentalization. Too many teachers reward a student who "gets" the right answer whether or not the student understands the context of the problem. A student who compartmentalizes recognizes a problem as a "calculation problem" and automatically reaches for a calculator. Similarly, a student will report a numerically accurate answer regardless of the context of the problem.

For example, suppose a cabinet has dimensions 6 feet high by 3 feet wide by 6 1/2" deep. Suppose a student is asked to determine how many full cases of 8 1/2" x 11" paper a cabinet will hold. One case (box and all) has dimensions 12"w x 18"l by 9" h. In an extreme case of compartmentalization a student will recognize a "volume problem" and report that the cabinet has volume of 16,848.0 cubic inches, and since each case has volume of 1944 cubic inches, the cabinet will hold 8.66666667 cases. Never mind that precision was grossly overstated. The cases were not to be broken up, and the cabinet is shallower than the smallest dimension of a case. A student who is aware of the context of the problem would see right away that the cabinet is not appropriate for such storage.

Most laboratory projects involve quantitative work. You are most likely to be successful if you know what numbers to expect and are aware of their significance.