CUSH: Main function for CUSH models

In CUB: A Class of Mixture Models for Ordinal Data

Main function for CUSH models

Description

Main function to estimate and validate a CUSH model for ordinal responses, with or without covariates to explain the shelter effect.

Usage

CUSH(Formula,data,...)

Arguments

Formula	Object of class Formula.
data	Data frame from which model matrices and response variables are taken.
...	Additional arguments to pass to the fitting procedure. Argument X specifies the matrix of subjects covariates to include in the model for explaining the shelter effect (not including intercept).

Details

The estimation procedure is not iterative, so a null result for CUSH$niter is produced. The optimization procedure is run via "optim". If covariates are included, the variance-covariance matrix is computed as the inverse of the returned numerically differentiated Hessian matrix (option: hessian=TRUE as argument for "optim"). If not positive definite, it returns a warning message and produces a matrix with NA entries.

Value

An object of the class "CUSH" is a list containing the following results:

estimates	Maximum likelihood parameters estimates
loglik	Log-likelihood function at the final estimates
varmat	Variance-covariance matrix of final estimates (if X=0, it returns the square of the estimated standard error for the shelter parameter \delta)
BIC	BIC index for the estimated model

References

Capecchi S. and Piccolo D. (2015). Dealing with heterogeneity/uncertainty in sample survey with ordinal data, IFCS Proceedings, University of Bologna
Capecchi S. and Iannario M. (2016). Gini heterogeneity index for detecting uncertainty in ordinal data surveys, Metron - DOI: 10.1007/s40300-016-0088-5

See Also

loglikCUSH

CUB documentation built on May 29, 2024, 5:23 a.m.