IRTLikelihood.cfa: Individual Likelihood for Confirmatory Factor Analysis

In TAM: Test Analysis Modules

Individual Likelihood for Confirmatory Factor Analysis

Description

This function computes the individual likelihood evaluated at a theta grid for confirmatory factor analysis under the normality assumption of residuals. Either the item parameters (item loadings L, item intercepts nu and residual covariances psi) or a fitted cfa object from the lavaan package can be provided. The individual likelihood can be used for drawing plausible values.

Usage

IRTLikelihood.cfa(data, cfaobj=NULL, theta=NULL, L=NULL, nu=NULL,
    psi=NULL, snodes=NULL, snodes.adj=2, version=1)

Arguments

data	Dataset with item responses
cfaobj	Fitted lavaan::cfa (lavaan) object
theta	Optional matrix containing the theta values used for evaluating the individual likelihood
L	Matrix of item loadings (if cfaobj is not provided)
nu	Vector of item intercepts (if cfaobj is not provided)
psi	Matrix with residual covariances (if cfaobj is not provided)
snodes	Number of theta values used for the approximation of the distribution of latent variables.
snodes.adj	Adjustment factor for quasi monte carlo nodes for more than two latent variables.
version	Function version. version=1 is based on a Rcpp implementation while version=0 is a pure R implementation.

Value

Individual likelihood evaluated at theta

See Also

CDM::IRT.likelihood

Examples

## Not run: 
#############################################################################
# EXAMPLE 1: Two-dimensional CFA data.Students
#############################################################################

library(lavaan)
library(CDM)

data(data.Students, package="CDM")
dat <- data.Students

dat2 <- dat[, c(paste0("mj",1:4), paste0("sc",1:4)) ]
# lavaan model with DO operator
lavmodel <- "
DO(1,4,1)
   mj=~ mj%
   sc=~ sc%
DOEND
   mj ~~ sc
   mj ~~ 1*mj
   sc ~~ 1*sc
     "
lavmodel <- TAM::lavaanify.IRT( lavmodel, data=dat2 )$lavaan.syntax
cat(lavmodel)

mod4 <- lavaan::cfa( lavmodel, data=dat2, std.lv=TRUE )
summary(mod4, standardized=TRUE, rsquare=TRUE )
# extract item parameters
res4 <- TAM::cfa.extract.itempars( mod4 )
# create theta grid
theta0 <- seq( -6, 6, len=15)
theta <- expand.grid( theta0, theta0 )
L <- res4$L
nu <- res4$nu
psi <- res4$psi
data <- dat2
# evaluate likelihood using item parameters
like2 <- TAM::IRTLikelihood.cfa( data=dat2, theta=theta, L=L, nu=nu, psi=psi )
# The likelihood can also be obtained by direct evaluation
# of the fitted cfa object "mod4"
like4 <- TAM::IRTLikelihood.cfa( data=dat2, cfaobj=mod4 )
attr( like4, "theta")
# the theta grid is automatically created if theta is not
# supplied as an argument

## End(Not run)

TAM documentation built on May 29, 2024, 2:20 a.m.