Raw Scores Are Not Linear Measures: : Rasch vs. Classical Test Theory CTT Comparison | ||
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Standing | Raw Scores | Linear Measures |
Psychometrics | Classical Test Theory CTT | Rasch Model RM |
Data | must be "complete" | robust against missing data and non-administered items |
Meaning | ordinal ranking on hoped-for latent variable | linear positioning on latent variable explicitly-defined by item content |
Status | mistaken for truth | known as estimates |
Additivity | non-linear, bent | linear, straight |
Continuity | discrete, lumpy | continuous, smooth |
Precision | unknown, except on average | quantified by standard errors |
Accuracy | unknown | quantified by local fit statistics |
Linear Analysis | unsuited to usual statistics | ideal for usual statistics |
Validity | sample-dependent test "reliability" | item-dependent construct validity |
Diagnosis | sample-dependent item point-biserial | individual item and person fit statistics |
Conceptualization | concrete | abstract |
Occurrence | accidental | deliberate |
Construction | irreproducible | reproducible |
Scope | local | general |
Relationships | incomparable | comparable |
Context | test-bound | test-free |
Integration | awkward to equate | simple to equate |
Benjamin D. Wright |
Raw Scores Are Not Linear Measures: : Rasch vs. Classical Test Theory CTT Comparison. B.D. Wright Rasch Measurement Transactions, 1992, 6:1, 208
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