Transcript Letter Grades.ppt

Assigning Letter Grades
based on Clustering
A Relative Grading Approach
By
Dr. Muhammad Elrabaa
COE Dept., KFUPM
Outline
What does a grade mean?
– Absolute vs. Relative grading
Human Perception of Grades: How fine
should our scale be?
A relative grading method based on
clustering
– An example
Conclusions
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What does a grade mean?
My understanding …
– Evaluation of a student’s level in a course
Measured against the intended course objectives
and outcomes
Should somehow be related to international
standards (what other students in similar courses
in other universities do)
– My professional assessment ‫شهادتي كمحترف‬
(should conform to ethical and moral
standard)
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What does a grade mean? Contd.
Absolute vs. Relative grading:
– Absolute grading:
Assessment is given on a numerical scale (out of
10, 20, 100 …etc.)
Meaningless unless standardized (national
exams, Professional societal exams or standard
questions with standard answers and grading)
If applied correctly could give an accurate
assessment of the program, department and the
whole institution
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What does a grade mean? Contd.
Absolute vs. Relative grading, Contd.
– Relative grading:
Assessment is relative to peers in the same class
Word assessment is usually used with some GPA
weights assigned for every grade (A=Excellent,
B=Very good, C= Average or Good, D=Weak,
F=Very Weak or Fail)
Should be understood within its context i.e.: An
“average” or C grade means that the student is on
par with the majority of his peers. A B grade means
the student is above average relative to his peers
and so on
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What does a grade mean? Contd.
Relative grading, Contd.:
– It is meaningless to say our average grade is
B! This amounts to saying our average
student is above the average with respect to
his peers (contradiction!)
– Hence the average grade, for a normal
sample, should come to be C~C+
– It takes a university tradition to concatenate
such grades with some absolute performance
measures for outsiders so e.g. employers
would assess our C as B of another institution
and so forth.
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Human Perception of Grades
How fine should our scale be?
– Humans tend to have a very limited capacity to
distinguish between relative performance levels
– We understand average, below average (weak),
above average (good) and distinguished (excellent). It
is not practical to expect us to understand the subtle
differences such as high-average, average, highweak, weak, high-very good, …etc.
– It is almost impossible to design exams and other
evaluation methods to distinguish between such
levels (C and C+, B and B+ or A and A+)
– Hence an A B C D F grading system is sufficient.
Finer resolution brings evaluation difficulties
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A clustering-based grading method
This is a relative grading method:
– Grades are sorted based on total scores
– Exclude extremes if they exist (Too high or too low):
40% above or 30% below the Average
– Cluster grades: A cluster is a group of grades with a
distinguishable difference from other clusters
– Start assigning grades from the top: ~25-30% above
the average is A+, then go down cluster by cluster
assigning grades. The F grade is usually ~15-20%
below the average and the total class average should
come to be between C and C+ and the class average
GPA is usually 2.1~2.5
– The above might be difficult to achieve for very large
samples (as in multi-sections) due to indistinguishable
clusters
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Example
Grading Example using Excel
1. Raw Grades
2. Sorted Grades
3. Assigned Grades
4. Final Grades
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Conclusions
Absolute grading is neither practical nor
possible
Relative grading should be taken as is: i.e.
relative. For it to be meaningful, the
average grade for a normal sample should
be between C and C+ (2 to 2.5)
Impossible to design exams that
distinguish performance at a fine
resolution  Clustering would ensure
some degree of fairness
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