CLAW FAQ - How are the marks curved?

In a large class with fair exams, the marks will roughly follow a Gaussian Probability Distribution, otherwise known as a Bell Curve. However, crafting an exam is not an exact science, and even the most experienced professors can sometimes make an exam too easy or too hard. A quick glance at the marks distribution (a plot of the number of students versus the marks received) will show how difficult an exam was. It is then up to the professor to decide how to assign the letter grades. This is usually done on a relative basis, by comparing each student's marks to the distribution curve, and deciding where the cut-offs are. This process is sometimes called "curving the marks". In other words, the marks are relative.

When are the marks curved?

Not until the end of the course. The letter grades are based upon the overall distribution for all the marks, including assignments, mid-term exams and the final exam.

What are the letter grade cut-offs?

The cut-offs are decided by the professor at the end of the course, by examining the overall marks distribution. The cut-offs are not generally made public because this causes distress to the students near the line. Remember, the line has to be drawn somewhere.

If marks are relative, how do I know how I'm doing?

Take a look at the distribution. Your marks are are available for you to view on the Web in GradeBook. Just click on the "Chart" icon within GradeBook to plot the distributions for all the assignments and exams. If you are near the top, you are doing well. If you are near the bottom, you're going to have to study harder.

What if we just happen to be a very smart class and all deserve A's?

For large classes, this is statistically very improbable.

What if it's a small class?

It's still up to the professor how to assign the marks. The professor may very well decide to give the whole class A's.

How can we beat the system?

Induce the whole class to slack off, bringing the whole distribution down, so that a mark of 50% corresponds to an "A"!

Will this work?

Probably not. Humans are basically competitive.

SFU / Math & Stats / ~hebron / claw / faq / curving.html

Revised 21 July 1999 by John Hebron.