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Rasch measurement converts dichotomous and rating scale observations
into linear measures. It links qualitative analysis to quantitative methods.
Rasch scaling is often classified under item response theory, IRT,
or logit-linear models. Rasch specifies how persons,
probes, prompts, raters, test items, tasks, etc. must interact statistically through probabilistic measurement models
for linear measures to be constructed from ordinal observations.
Rasch analysis requires the investigation and quantification of accuracy,
precision, reliability, construct validity, quality-control fit statistics,
statistical information, linearity, local dependency and unidimensionality. Rasch
implements stochastic Guttman ordering, conjoint additivity, Campbell
concatenation, sufficiency and infinite divisibility.
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