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Q&A #356

Teachers' Lounge Discussion: Curving test scores

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From: RON <rselby@cinci.rr.com>
To: Teacher2Teacher Public Discussion
Date: 2003060217:22:37
Subject: Re: curving test scores

SEVERAL POINTS:

THE PURPOSE OF CURVING A TEST IS NOT TO HELP THE STUDENTS TO ACHIEVE A
HIGHER SCORE. THE IDEA IS TO HAVE A COMPARISON OF STUDENTS RELATIVE
ACHIEVEMENTS TO EACH OTHER ( PREFERABLY IN A LARGE GROUP). THE
ASSIGNMENT OF GRADES ( PERCENT, LETTER, ETC.) IS DETERMINED NOT ON AN
PRESET SCALE, BUT ON A SCALE DETERMINED BY THE RESULTS OF THE TEST.
THIS METHOD ALLOWS TESTING WITH A GROUP OF QUESTIONS WHICH HAVE NOT
BEEN SHOWN TO BE STATISTICALLY VALID.

THE BASIC PREMISE IS THAT THE RAW SCORES OBTAINED BY THE GROUP OF
STUDENTS WILL FIT A NORMAL DISTRIBUTION ( BELL CURVE). THE MEAN AND
STANDARD DEVIATION ARE COMPUTED AND THE RAW SCORES ARE THEN
TRANSFORMED INTO STANDARD NORMAL RESULTS. IT IS THESE TRANSFORMED
SCORES THAT ARE ASSIGNED A GRADE.

THE IDEA THAT A CURVE ON A TEST SHOULD ONLY BE USED WHEN TEST RESULTS
ARE BELOW THE DESIRED LEVEL IS ONE CREATED BY PEOPLE WHO WISH TO
ARTIFICIALLY INFLATE THE GRADES OF STUDENTS. THIS MAKES STUDENTS
APPEAR TO BE ACHIEVING AT A HIGHER LEVEL THAN IS ACTUALLY THE CASE.

IF CURVING TEST RESULTS IS A PRACTICE TO BE USED, THEN ALL TESTS
SHOULD BE CURVED. THIS CAN PRODUCE SOME UNDESIRED GRADING RESULTS FOR
THOSE WHO THINK THAT GIVING HIGHER GRADES IS BENEFICIAL TO STUDENTS.
FOR EXAMPLE, IF A TEST IS GIVEN AND THE MEAN SCORE IS 95/100, THEN
THAT WOULD IMPLY THE AVERAGE STUDENT (OR "C" STUDENT) WOULD GET
APPROXIMATELY THAT SCORE. NOT MANY EDUCATORS ARE WILLING TO GIVE A
STUDENT A GRADE OF "C" FOR GETTING A SCORE OF 95/100 ON A TEST, BUT
THAT IS PRECISELY WHAT SHOULD OCCUR IF CURVING TEST SCORES IS TO BE
USED. OTHERWISE, IF THE GRADES ARE ONLY TO BE RAISED AND NOT TO BE
LOWERED BY CURVING SCORES INSTEAD OF USING A PRESET SCALE, THE OVERALL
EFFECT IS TO INFLATE STUDENTS GRADES BEYOND THEIR ACTUAL VALUE.

PERHAPS SOMEONE AT YOUR SCHOOL HAS STUDIED STATISTICS AND COULD HELP
WITH THE APPROPRIATE COMPUTATIONS. IF NOT, I SUGGEST SOME READING ON
THE STANDARD NORMAL PROBABILITY DISTRIBUTION AND HOW TO MAKE
TRANSFORMATIONS FROM OTHER NORMAL DISTRIBUTIONS. THE COMPUTATIONS ARE
NOT VERY DIFFICULT AND SEVERAL HAND HELD CALCULATORS HAVE
PREPROGRAMMED FUNCTIONS FOR EXACTLY THAT.

ONE OTHER CONCERN IS THAT APPARENTLY ALL TEACHERS ARE NOT DEVOTING THE
SAME AMOUNT OF TIME OR PRIORITY TO THE SAME ITEMS OF THE CURRICULUM. 
IF IT IS THE POLICY OF YOUR SCHOOL THAT ALL TEACHERS SHOULD TEACH THE
SAME CURRICULUM FOR THE PURPOSE OF GIVING ALL STUDENTS THE SAME TESTS,
THEN THE FACULTY NEEDS TO BE VERY DILIGENT IN FOLLOWING THE PROGRAM.
OTHERWISE, AS YOU INDICATED, SOME STUDENTS WILL BE AT A DISADVANTAGE
WHEN TEST TIME COMES AROUND.


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