PARAMTER ESTIMATION

Question:

What estimation algorithm is employed in RUMM2030?

Explanation:

When conducting a Rasch analysis, RUMM2030 uses the "Pairwise Conditional Estimation procedure" which generalises the equation for one pair of items in which the person parameter is eliminated to all pairs of items taken simultaneously.

Pairwise estimation is conditional estimation in the sense that the person parameters are eliminated while the item parameters are estimated. The estimates are consistent see

Zwinderman, A, H. (1995). Pairwise estimation in the Rasch models. Applied Psychological Measurement, 19,4, 369 - 375.

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Question:

Why is the spread of the item estimates in RUMM2030 smaller than with other Rasch Applications?

Explanation:

As the algorithm in RUMM2030 is the pairwise conditional, it would be expected that this spread would not be as large as for algorithms using what is essentially the unconditional or joint method. The level of precision with respect to the convergence criterion will also influence the spread.

If the convergence criterion is made more precise by changing from, say, 0.01, to 0.001 or 0.0005, then the estimates in RUMM2030 will spread out a bit more.

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