by John M. Linacre
MESA Research Note 6, November 1998
The Rasch model is based on the non-linear logistic function. In general, estimates for measures cannot be obtained directly, but must be obtained through a process of improving estimates until they are good enough ("converged"). The process requires performing the same computations over and over again ("iteration").
The iterative process is shorter when:
In one data set with very adverse characteristics, over 600 iterations were required before meaningful estimates were obtained.
In many cases, the estimates are good enough after only a few iterations. A large number of iterations may only be needed for the final, definitive analysis.
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