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
                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
                                       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
                                       Did not reach end of test?
                                       Only answered easy items?
Judge Rating    Noisy  Noisy    Extreme category overuse
                                       Extremism? Defiance?
                Muted  Muted    Middle category overuse
                                       Conservatism? Resistance?
Judge Rating    Muted  Muted    Apparent unanimity
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

Rasch Publications
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
in Spanish: Análisis de Rasch para todos, Agustín Tristán Mediciones, Posicionamientos y Diagnósticos Competitivos, Juan Ramón Oreja Rodríguez

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