MxCI is an S4 class. An MxCI object is a named entity. New instances of this class can be created using the function mxCI. MxCI objects may be used as arguments in the mxModel function.
The MxCI class has the following slots:
|The name of the object
|Either a matrix or a data frame
|A vector for means, or NA if missing
The reference slot contains a character vector of named free parameters, MxMatrices and MxAlgebras on which confidence intervals are desired. Individual elements of MxMatrices and MxAlgebras may be listed as well, using the syntax “matrix[row,col]” (see Extract for more information).
The lowerdelta and upperdelta slots give the changes in likelihoods used to define the confidence interval. The upper bound of the likelihood-based confidence interval is estimated by increasing the parameter estimate, leaving all other parameters free, until the model -2 log likelihood increased by ‘upperdelta’. The lower bound of the confidence interval is estimated by decreasing the parameter estimate, leaving all other parameters free, until the model -2 log likelihood increased by ‘lowerdata’.
Likelihood-based confidence intervals may be specified by including one or more MxCI objects in an MxModel object. Estimation of confidence intervals requires model optimization using the mxRun function with the ‘intervals’ argument set to TRUE. The calculation of likelihood-based confidence intervals can be computationally intensive, and may add a significant amount of time to model estimation when many confidence intervals are requested.
The OpenMx User's guide can be found at http://openmx.psyc.virginia.edu/documentation.
mxCI for creating MxCI objects. More information about the OpenMx package may be found here.