R/model4.R

In markhwhiteii/processr: R Implementation of the PROCESS Macro

#' Model 4 from the PROCESS Macro: Simple Mediation
#' 
#' This function will perform simple mediation, using the `lavaan` package.
#' It uses bias-corrected bootstrap resampling for the confidence intervals.
#' 
#' @param iv The name of the independent variable, as a character string.
#' @param dv The name of the dependent variable, as a character string.
#' @param med The name of the mediator, as a character string.
#' @param data The data frame with the relevant variables.
#' @param samples The number of bootstrap resamples. Defaults to 5000.
#' @return Coefficients, standard errors, z-values, p-values, and confidence intervals
#' for all estimated parameters. The indirect effect will not return standard errors,
#' z-values, or p-values.
#' @export
model4 <- function(iv, dv, med, data, samples = 5000) {
  model <- paste0(
    med, " ~ a * ", iv, "\n", 
    dv, " ~ b * ", med, " + cp * ", iv, "\n",
    "ind := a * b\nc := cp + a * b"
  )
  
  out <- lavaan::parameterEstimates(
    lavaan::sem(model = model, data = data, se = "boot", bootstrap = samples),
    boot.ci.type = "bca.simple"
  )
  
  out[7 ,6:8] <- NA
  out <- out[c(1, 2, 3, 7, 8), 4:10]
  rownames(out) <- 1:nrow(out)
  
  return(out)
}