[Rasch] Explaining diferences in scores and measures

Burga León Andrés Alberto 21781 at upch.edu.pe
Sat Mar 8 04:15:32 EST 2008


Hello to everybody on the list:
 
I hope you could helop me explaining the situation I have aboput the diferences in measures and scores.
 
I'm working with two diferent test (math and reading), made of 24 items. The objective is to use the mesure in order to calsify each student into a proficiency level. We have two cut-point for each test ( so tree proficiency levels). If a student have a greater than 0.62 probability of giving a correct answer to the cut-point item, he is classified into that proficciency level.
 
I have this same situation in both test. For example, the first cut score is on the 11th item. A student with a 0.62 propability of answering that items must have 13 correct items on the test. The second cut score is on the 23th item. A student with a 0.62 propability of answering that items must have 21 correct items on the test.
 
Why for the first cur score a sudent need more correct answer (13) than the cut score (11th item) and for the second cut score he need less correct answer (21) than the cut scores (23th item)? I found this dificult to explain.
 
Kindly
 
Andres
 
 



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