lavaan (version 0.5-17)

lavTestWald: Wald test

Description

Wald test for testing a linear hypothesis about the parameters of fitted lavaan object.

Usage

lavTestWald(object, constraints = NULL, verbose = FALSE)

Arguments

object

An object of class lavaan.

constraints

A character string (typically between single quotes) containing one or more equality constraints. See examples for more details.

verbose

Logical. If TRUE, print out the restriction matrix and the estimated restricted values.

Value

• A list containing three elements: the Wald test statistic (stat), the degrees of freedom (df), and a p-value under the chi-square distribution (p.value).

Details

The constraints are specified using the "==" operator. Both the left-hand side and the right-hand side of the equality can contain a linear combination of model parameters, or a constant (like zero). The model parameters must be specified by their user-specified labels. Names of defined parameters (using the ":=" operator) can be included too.

Examples

HS.model <- '
    visual  =~ x1 + b1*x2 + x3
    textual =~ x4 + b2*x5 + x6
    speed   =~ x7 + b3*x8 + x9
'

fit <- cfa(HS.model, data=HolzingerSwineford1939)

# test 1: test about a single parameter
# this is the 'chi-square' version of the 
# z-test from the summary() output
lavTestWald(fit, constraints = "b1 == 0")

# test 2: several constraints
con = '
   2*b1 == b3
   b2 - b3 == 0
'
lavTestWald(fit, constraints = con)