[Rasch] Fan: raw scores and Rasch

Mike Linacre (RMT) rmt at rasch.org
Tue Oct 30 10:53:46 EST 2007

Quote: "There simply is little appreciable difference between raw score 
sums and the Rasch model,"

Except when there is an appreciable difference!

For instance, when there is missing data ...

Or when the floor and ceiling effects of raw score sums are producing 
misleading inferences. In one study, a raw-score "ceiling effect" was being 
misunderstood as "the therapy has stopped being cost-effective". In fact, 
the therapy was increasingly cost-effective.

Or when instruments must be equated. Even the great statistician, John 
Tukey, misequated samples based on raw-score-percentages, producing 
nonsense results: www.rasch.org/rmt/rmt64m.htm

Mike L.

Mike Linacre
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT:  21:1 Summer 2007
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