Estimating A Path Model With Lavaan

## Written by Ian A. Silver
## Written on 11.4.2020
## Estimating a three variable path model with Lavaan

# Getting Started ####
library(pastecs)
library(lavaan)

options(scipen=100, digits=6)
options(max.print = 500000000)
# Loading Data (THE DIRECTORY SHOULD CHANGE) ####
## You can find the directory for the file by right clicking on the file and clicking on the properties option
A<-read.csv("C:/Desktop/Mediation Path Data.csv") #Personal Directory should be placed for the data file (make sure you use "/")


# Estimating A Mediated Path Model With Lavaan ####

stat.desc(A) # Provides descriptive statistics for all of the variables in the dataframe

#Creating the formula for the Lavaan Model
F<-'

# First Equation Z (mediator) regressed on X (exogenous variable)
Z~a*X # "a*" informs Lavaan to save the estimate as the letter "a"

# Second equation Y (endogenous variable) regressed on Z (mediator) and X (exogenous variable)
Y~b*Z+c*X # "b*" informs Lavaan to save the estimate as the letter "b"; "c*" informs Lavaan to save the estimate as the letter "c"

# Calculating the Indirect effects (the path from X to Z multiplied by the path from Z to Y)
ab := a*b # SE, p-values, and CI are calculated using the delta method (Described in Sobel 1982)

# Calculating the total effects(the path from X to Y plus the path from X to Z multiplied by the path from Z to Y)
abc := c+(a*b) # SE, p-values, and CI are calculated using the delta method (Described in Sobel 1982)
'

# Estimating the Model
M<-sem(F, data = A, estimator = "ML")

# Summary of the Results
## The summary provides: Global fit statistics, Regression Estimates, residual variances, direct and indirect estimates, and standardized estimates
print(summary(M, standardized = TRUE, ci = TRUE))


# Residuals
print(resid(M, type = "cor"))

# Modification indices
print(modindices(M)) # produced in a manner similar to MPLUS

## Citation
# Sobel M. E. (1982). Asymptotic confidence intervals for indirect effects in structural equation models. Sociological Methodology 13, 290-312.