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help for geekel2d                                          Jean-Benoit Hardouin
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Estimation of the parameters of undimensional and bidimensional IRT models

geekel2d varlist [, coef(matrixname) nbit(#) critconv(#) ll

varlist is a list of two existing dichotomous variables or
more.

Description

geekel2d estimates, by Generalized Estimating Equations (GEE), the
parameters of the model defined by Kelderman (1994) with one or two
dimensions and dichotomic items. This model includes the Rasch model
and the One Parameter Logistic Model (OPLM) for the unidimensional
models, the Multidimensional Generalized Rasch Model (MGRM) and the
Multidimensional Completely Sufficient Rasch Model (MMSRM) for the
two-dimensional models.

Options

coef is the name of a matrix which contains the coeficients B. This
matrix relies the items and the latent traits. Each row represents an
item and there is as many colmuns than the supposed number of latent
traits (one or two).  The coefficients are choosen, in general, among
the first intergers, but geekel2d allows using real coefficients. By
default, the Rasch model is supposed (the matrix coef is a vector of
1).

nbit defines the maximal number of iterations in the estimation
algorithm. By default, this number is fixed to 30.

critconv is the value of the convergence criterion, calculated as the
square of the cross-product of the vector containing the difference
between two successive iterations of the parameters estimations. By
default, this criterion is fixed to 1e-15.

ll estimates the marginal log-likelihood and the Akaike Information

novar avoids to compute the standards errors of the estimators (faster).

Remarks

For detailed informations on the Kelderman model, see Kelderman and
Rijkes (1994) or Adams and al. (1997).

geekel2d don't allows using of polytomous items.

The ghquadm Stata module is needed (use findit ghquadm to obtain it).

Example

. geekel2d item1 item2 item3 item4 /*Rasch model*/

. matrix B=(1,0\1,0\0,1\0,1)

. geekel2d item1 item2 item3 item4 , coef(B) nbit(50) critconv(1e-30)

References

Kelderman H. and Rijkes C. P. M., Loglinear multidimensional IRT models
for polytomously scored items. Psychometrika, 1994, 59, 149-176.

Adams R. J., Wilson M. R. and Wang W., The multidimensional random
coefficient multinomial logit model. Applied Psychological
Measurement, 1997, 21, 1-23.

Author

Jean-Benoit Hardouin, Regional Health Observatory (ORS) - 1, rue Porte
Madeleine - BP 2439 - 45032 Orleans Cedex 1 - France. You can contact
the author at jean-benoit.hardouin@orscentre.org and visit the
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