To measure the person, not the test

In spite of most of what has been said up to this point, we did not undertake this project with the hope of building better thermometers. The point is to measure the person. Because of the complete symmetry of the model, everything we have done for items, we can do again for people just by reversing the subscripts. For any two people who took some of the same items, count the number *N*_{12} that person *2* answered correctly and person *1* missed; also the number *N*_{21} that person *1* passed and person *2* missed. The relative abilities of the people will parallel expressions 23 and 25:

Continue reading . . .The Point is Measurement

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It has come to my attention that equation 39 has a plus sign where it should have a minus. It has been corrected and now the arithmetic makes sense.

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