semTools (version 0.4-13)

SSpower: Power for model parameters

Description

Determines power for model parameters using the Satorra & Sarris (1985) method

Usage

SSpower(popModel, n, powerModel, fun = "cfa", nparam = 1, alpha = .05, ...)

Arguments

popModel

lavaan syntax for the population model. This model should specify population values for all paramters in the model.

n

Sample size used in power calculation

powerModel

lavaan syntax for the model to be analyzed. This syntax should have the parameter(s) of interest fixed to 0 (or some other number).

fun

The character of the function name used in running lavaan model ("cfa", "sem", "growth", "lavaan").

nparam

The number of parameters one is constrained in powerModel.

alpha

The Type I error rate used to assess power

...

Other arguments to be passed to the specified lavaan function ("cfa", "sem", "growth", "lavaan").

References

Satorra, A., & Saris, W. E. (1985). Power of the likelihood ratio test in covariance structure analysis. Psychometrika, 50, 83-90.

Examples

library(lavaan)

#Specify population values. Note every paramter has a fixed value
modelP <- '
         f1 =~ .7*V1 + .7*V2 + .7*V3 + .7*V4
         f2 =~ .7*V5 + .7*V6 + .7*V7 + .7*V8
         
         f1 ~~ .3*f2
         f1 ~~ 1*f1
         f2 ~~ 1*f2
         
         V1 ~~ .51*V1
         V2 ~~ .51*V2
         V3 ~~ .51*V3
         V4 ~~ .51*V4
         V5 ~~ .51*V5
         V6 ~~ .51*V6
         V7 ~~ .51*V7
         V8 ~~ .51*V8  
         '

#Specify model to be analyzed. Note parameter of interest f1~~f2 is fixed to 0.
modelA <- '
         f1 =~ V1 + V2 + V3 + V4
         f2 =~ V5 + V6 + V7 + V8
         
         f1 ~~ 0*f2

  
         '

	
SSpower(modelP, 150, modelA, std.lv=TRUE)

##Get power for a range of values

Ns <- seq(100, 500, 40)
powVals <- rep(NA, length(Ns))
for(i in 1:length(Ns)){
powVals[i] <- SSpower(modelP, Ns[i], modelA)
}
plot(Ns, powVals, type = 'l')