There are times when a professor wishes to raise or lower his or her students' grades.
Perhaps a directive has come down from on high: "Instructors need to focus on increasing student success rates." "The average grade in this class is above the departmental norm - grades must come down."
Or a professor might wish to maximize teaching evaluations while maintaining a reputation for rigor and standards using the tried-and-true easy midterm/killer final technique.
Grades can be manipulated with curving: moving grades up (students rarely object) or down (students will definitely object). Yet curving gives the impression that grading is arbitrary or subjective.
A far better approach is to manipulate grades through strategic exam setting. For the young, carefree or otherwise uninitiated, here is a simple demonstration.
Let's start out with a classic undergraduate question designed to test whether or not students understand consumer choice theory. A question that would produce relatively low grades is something like:
Short answer questions:
1) True, false or uncertain: a tax on gasoline will reduce the quantity of gasoline demanded.
The first thing that makes this question so difficult is that no information has been given about the type of answer required. Good students will know that an explanation and a diagram is expected, but some hapless souls will think a simple "True" or "False" will suffice, and get 0 or 1 out of ten for their efforts.
I've had this conversation one too many times: "Yes, you wrote down uncertain, and that's the right answer, but simply writing uncertain is not enough." "But Prof, it didn't say that I had to add an explanation and draw a diagram, I gave you everything you asked for."
The examination ends up being more enjoyable for everyone involved if students are nudged in the right direction:
1) True, false or uncertain: a tax on gasoline will reduce the quantity of gasoline demanded. Your answer should include a diagram and a paragraph of explanation.
When presented with the question above, a significant percentage of students will draw a demand curve and say something along the lines of "demand curves slope down, therefore a tax on gasoline will reduce the quantity demanded." This answer is unsatisfactory because it fails to give any coherent theoretical explanation as to why demand curves slope downwards - and getting at the underlying why is the point of the question.
A professor hoping for a life that is quiet and complaint-free might be advised to clarify the question further:
1) True, false or uncertain: a tax on gasoline will reduce the quantity of gasoline demanded. Your answer should include an indifference curve/budget constraint diagram and a paragraph of explanation.
This small change in wording will produce a completely different set out of answers - almost every student will produce an answer with some kind of indifference curve/ budget constraint diagram. Yet a significant percentage will still fail to provide a good answer because of the "true, false and uncertain" component.
Answering true, false or uncertain questions correctly requires a basic knowledge of logic. One counter-example - one situation in which the quantity of gas demanded does not change, or even increases, after the tax - is sufficient to prove a statement false. No number of cases in which gasoline taxes cause the quantity demanded to fall are sufficient to prove the statement universally true. Students can't be blamed for not knowing this - logic is not a formal part of the high school or university curriculum.
The best way to promote student success is to phrase the question like this:
1) Using an indifference curve/budget constraint diagram, show that it is possible for a tax on gasoline to have no effect on the quantity of gasoline purchased. Explain.
Clear, unambiguous - what's not to like?
When grading students, one can make two types of errors. The first is to give poor grades to students who understand the material, but were misled by unclear or ambiguous questions. The second is to give high marks to students who do not understand the underlying concepts, but were able to memorize and reproduce the material presented in the lectures and readings. The optimal exam question will balance off these two sources of error, striking some kind of middle ground between obscurity and obviousness.