"The Rasch model is too rigid." "It demands too much from our data." "It throws out too many items." Perhaps the Rasch model is a mathematical Maud:
Perfectly beautiful: let it be granted her:
where is the fault?
Faultily faultless, icily regular, splendidly null.
Dead perfection, no more.
Are Rasch analysts wrong to seek perfection? The book, "The Customer is the Key" (M.M. Lee with J.N. Sheth, Wiley, 1991) describes the six characteristics of businesses identified as "winners". They are summarized thus:
Fig. 1. Six key characteristics of "winning" businesses. (redrawn from Fig. 3.1, Lele & Sheth, 1991).
Notice the extreme language, "impossible", "obsessive", "everyone", "maximize." Surely no business can actually achieve these characteristics? Lele & Sheth admit that they can't, but "these companies realize that performance often falls short of expectations. Therefore, in order to deliver merely good results, they must set their sights on impossible goals. .... knowing that they are likely to achieve something less than what they aim for is the most compelling reason that they can give for aiming for the best" (p. 61). This suggests that Fig. 1 also applies to "winning" measurement projects, see Fig.2:
Fig. 2. Six key characteristics of "winning" measurement projects. (after Lele & Sheth, 1991).
"Science must begin with myths." (Alexander Pope)
"Yours is a distinctive vision, you believe. And it's also ideal. After all, you want to set a new standard of perfection, beauty or excellence. You want to be a model for others. Yours is an ideal and unique image of the future" (J.M Kouzes & B.Z. Posner, The Leadership Challenge, Jossey-Bass, 1995, p. 96)
Let our myth be that perfection is attainable, and let us resist the shame of having mediocrity thrust upon us (Joseph Heller, Catch-22).
John Michael Linacre
Rasch model and the quest for perfection, Lee M, Sheth J, Linacre J Rasch Measurement Transactions, 2004, 18:3 p. 985
|Rasch Measurement Transactions (free, online)||Rasch Measurement research papers (free, online)||Probabilistic Models for Some Intelligence and Attainment Tests, Georg Rasch||Applying the Rasch Model 3rd. Ed., Bond & Fox||Best Test Design, Wright & Stone|
|Rating Scale Analysis, Wright & Masters||Introduction to Rasch Measurement, E. Smith & R. Smith||Introduction to Many-Facet Rasch Measurement, Thomas Eckes||Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, George Engelhard, Jr.||Statistical Analyses for Language Testers, Rita Green|
|Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar||Journal of Applied Measurement||Rasch models for measurement, David Andrich||Constructing Measures, Mark Wilson||Rasch Analysis in the Human Sciences, Boone, Stave, Yale|
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