Diagnosing Misfit

------------------------------------------------------------------ Classification INFIT OUTFIT Explanation Investigation ------------------------------------------------------------------ Hard Item Noisy Noisy Bad item Ambiguous or negative wording? Debatable or misleading options? Muted Muted Only answered by top people At end of test? ------------------------------------------------------------------ Item Noisy Noisy Qualitatively different item Incompatible anchor value Different process or content? Anchor value incorrectly applied? ? Biased (DIF) item Stratify residuals by person group? Muted Curriculum interaction Are there alternative curricula? ------------------------------------------------------------------ Muted ? Redundant item Similar items? One item answers another? Item correlated with other variable? ------------------------------------------------------------------ Rating scale Noisy Noisy Extreme category overuse Muted Muted Middle category overuse Poor category wording? Combine or omit categories? Wrong model for scale? ------------------------------------------------------------------ Person Noisy ? Processing error Clerical error Idiosyncratic person Scanner failure? Form markings misaligned? Qualitatively different person? ------------------------------------------------------------------ High Person ? Noisy Careless Sleeping Rushing Unexpected wrong answers? Unexpected errors at start? Unexpected errors at end? ------------------------------------------------------------------ Low Person ? Noisy Guessing Response set "Special" knowledge Unexpected right answers? Systematic response pattern? Content of unexpected answers? Muted ? Plodding Caution Did not reach end of test? Only answered easy items? ------------------------------------------------------------------ Person/ Judge Rating Noisy Noisy Extreme category overuse Extremism? Defiance? Muted Muted Middle category overuse Conservatism? Resistance? ------------------------------------------------------------------ Judge Rating Muted Muted Apparent unanimity Collusion? ------------------------------------------------------------------ INFIT: information-weighted mean-square, sensitive to irregular inlying patterns
OUTFIT: usual unweighted mean-square, sensitive to unexpected rare extremes
Muted: unmodelled dependence, redundance, error trends
Noisy: unexpected unrelated irregularities

See Wright & Stone, Best Test Design, p. 2-4, 66-82, 23-24, 121-125, 165-190, and Wright & Masters, Rating Scale Analysis, p. 19-23, 94- 105, 108-111 for basics, and 132-135, 147-151, 171-178, 190-198 for examples.

Diagnosing Misfit, B Wright … Rasch Measurement Transactions, 1991, 5:2 p. 156

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