Unfolding data for unidimensional variables constructed
from direct responses (e.g., agreement or disagreement)
are characterized by single peaked functions
involving the locations of each person and each
stimulus. A continuous discrirninal process, of the
form postulated by Thurstone when he proposed his
Law of Comparative Judgment, is suggested. This
process is transformed to a qualitative dichotomous response
in which the probability of endorsement is
governed by the square of the distance between the locations
of the person and the stimulus. Maximum likelihood
estimates of the parameters are derived, and it
is shown that the information associated with any response
is a bimodal function of the difference between
the person and stimulus locations. The feasibility of
parameter estimation is demonstrated with a limited
simulation study. The model is applied to a set of
statements designed to measure attitudes toward capital
punishment and scaled by the methods of Thurstone.
The responses conformed to the unfolding
mechanism, and the scale values of the statements are
statistically equivalent to those obtained by Thurstone’s
methods. Index terms: Attitude measurement,
Developmental data, Discriminal process, Item
response theory, Person response theory, Thurstone
scaling, Unfolding data, Unidimensional scaling.
Andrich, David. (1988). The application of an unfolding model of the PIRT type to the measurement of attitude. Applied Psychological Measurement, 12, 33-51. doi:10.1177/014662168801200105
The application of an unfolding model of the PIRT type to the measurement of attitude.
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