The θ scale in item response theory has arbitrary
unit and origin. When a group of items is calibrated
twice, estimates from one calibration must be transformed
to the metric of the other. A new method is
presented for doing so. It is simpler than an earlier
method based on test characteristic curves, and makes
more complete use of available information.
Divgi, D. R. (1985). A minimum chi-square method for developing a common metric in item response theory. Applied Psychological Measurement, 9, 413-415. doi:10.1177/014662168500900410
Divgi, D. R..
A minimum chi-square method for developing a common metric in item response theory.
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