In a way, yes, they were superseded. There is a school of thought now
in which the proponents would argue (imv successfully) that the
approach you’ve outlined culminated in Rasch’s Simple Logistic Model.
Over and above the benefits of the Thurstone’s comparative judgements,
the Rasch model allows you to place person parameters and item
parameters on the one metric, and to eliminate person parameters in the
estimation of item parameters, and vice versa. Most importantly,
according to proponents, the model allows you to achieve the
requirements of fundamental measurement (including conjoint additivity
and invariance --I can give some explanation and/or quotes if you like)
provided a reasonable fit of data to the model.
The Rasch model is a stochastic one in which responses are said to be
governed only by a person parameter and an item parameter. While
Thurstone used the normal curve in his law of comparative judgement,
Rasch used the logistic approximation (very close of course). Tthis
allowed him to separate person and item parameters – a very significant
achievement imv. In turn, he called the outcome ‘specific
objectivity’. That is, the estimates of item parameters are
independent of the particular set of persons used to derive them, and
the estimates of person parameters are independent of the particular
set of items used to derive them (this is algebraic fact under the
model, then the point is – do the data fit the model?). Such
objectivity is key in the physical sciences (I have a quote in which
Andrich (see below) shows how this situation applies for a = f/m,
whereby a comparison of accelerations is independent of the force that
is instrumental in causing them).
There are various sources of information on this. Try www.rasch.org/
for some discussion of the properties of the Rasch model, applications,
and various other things. Or there is “Rasch Models for Measurement”
by David Andrich. But there are various refs on the above website. If
you want to know anything more, just ask, and I’ll help if I can –
though I’m relatively new to Rasch myself (I’ve done courses with David
Andrich, who developed the ‘Extended Logistic Model’ for use with
Likert scale data rather than dichotomous data, and himself trained
with Rasch for a time).
Take care,
Steve
Sent via Deja.com http://www.deja.com/
Before you buy.
===========================================================================
This list is open to everyone. Occasionally, less thoughtful
people send inappropriate messages. Please DO NOT COMPLAIN TO
THE POSTMASTER about these messages because the postmaster has no
way of controlling them, and excessive complaints will result in
termination of the list.
For information about this list, including information about the
problem of inappropriate messages and information about how to
unsubscribe, please see the web page at
http://jse.stat.ncsu.edu/
===========================================================================
