indirect_proportion function

Proportion of Effect Mediated

It computes the proportion of effect mediated along a pathway.

indirect_proportion(x, y, m = NULL, fit = NULL)

Arguments

• x: The name of the x variable. Must be supplied as a quoted string.
• y: The name of the y variable. Must be supplied as a quoted string.
• m: A vector of the variable names of the mediator(s). The path goes from the first mediator successively to the last mediator. Cannot be NULL for this function.
• fit: The fit object. Can be a lavaan::lavaan object or a list of lm() outputs. It can also be a lavaan.mi object returned by semTools::runMI() or its wrapper, such as semTools::sem.mi().

Returns

An indirect_proportion class object. It is a list-like object with these major elements:

• proportion: The proportion of effect mediated.
• x: The name of the x-variable.
• y: The name of the y-variable.
• m: A character vector of the mediator(s) along a path. The path runs from the first element to the last element.

This class has a print method and a coef method.

Details

The proportion of effect mediated along a path from x to y is the indirect effect along this path divided by the total effect from x to y

(Alwin & Hauser, 1975). This total effect is equal to the sum of all indirect effects from x to y

and the direct effect from x to y.

To ensure that the proportion can indeed be interpreted as a proportion, this function computes the the proportion only if the signs of all the indirect and direct effects from x to y

are same (i.e., all effects positive or all effects negative).

Examples

library(lavaan)
dat <- data_med
head(dat)
mod <-
"
m ~ x + c1 + c2
y ~ m + x + c1 + c2
"
fit <- sem(mod, dat, fixed.x = FALSE)
out <- indirect_proportion(x = "x",
                           y = "y",
                           m = "m",
                           fit = fit)
out

References

Alwin, D. F., & Hauser, R. M. (1975). The decomposition of effects in path analysis. American Sociological Review, 40(1), 37. tools:::Rd_expr_doi("10.2307/2094445")

See Also

print.indirect_proportion()

for the print method, and coef.indirect_proportion() for the coef method.