Using "mxAlgebras" to compare indirect effects

Hi community,

I am currently using the wls() function from the MetaSEM package to conduct mediation analysis with two parallel mediators. My code successfully estimates the indirect effects and their significance using likelihood-based confidence intervals. However, I am curious about estimating the difference between these indirect effects (e.g., between the two indirect effects).

I attempted to write a function such as a1b1 - a2b2, and it produced results. Now, I am wondering how reliable this practice is, as I have found little mention of it in Mike’s book and seminars.

Here is my code for reference:

MASEM_df2_Total_Effect <- wls(
  Cov = corr_df, 
  aCov = acov_df, 
  n = sample_size, 
  diag.constraints = TRUE, 
  RAM = RAM, 
  cor.analysis = TRUE, 
  intervals.type = "LB",
  mx.algebras = list(
    Total = mxAlgebra(b12 * b24 + b13 * b34 + b14, name = "Total"),
    Indirect_total = mxAlgebra(b12 * b24 + b13 * b34, name = "Indirect_total"), 
    Indirect_1 = mxAlgebra(b12 * b24, name = "Indirect_1"),
    Indirect_2 = mxAlgebra(b13 * b34, name = "Indirect_2"),
    Indirect_diff = mxAlgebra(b12 * b24 - b13 * b34, name = "Indirect_diff")
  )
)

Best regards,
Jennis