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PDT Gain Factor



At the Anaheim AAPT meeting someone gave a talk on the g factor for the
PTD (FCI) exam. The traditional g factor is

g = (posttest - pretest) / (30 - prestest)

where 30 is a perfect score. The problem will this g factor is that one
set of scores can provide a disproportional impact on the classes g-factor
average. This only happens when the pretest score is high and the postest
score is less high. For example, if the pretest score is 29 and the
posttest score is 26 the traditional g factor is -4. Since the maximum
possible g factor is +1, a g factor of -4 has a disproportionate impact on
the class average. The situation is even worse if the pretest score is a
perfect 30. Then, a less then perfect posttest score give a traditional g
factor of NAN (Not A Number) since the denominator is zero.

Anyway, the speaker proposed an improved g factor that avoided such
disproportionate impacts. Unfortunately, I forgot it. Can
someone out with a better memory than mine tell me what it is?

Gene

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Eugene (Gene) P. Mosca Phone 410-293-6659 Office
Physics Department 410-267-0144 Home
572 Holloway Road 610-683-3597 Summer
U.S.Naval Academy Mailstop 9C, Michelson Rm 339
Annapolis MD 21402 email: mosca@nadn.navy.mil
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