Assess if a variable confounds a relationship

Assess if a variable confounds a relationship

Usage

is_confounder(.tdy_dag, z, x, y, direct = FALSE)

Arguments

.tdy_dag

A tidy_dagitty or dagitty object

z

a character vector, the potential confounder

x, y

a character vector, the variables z may confound.

direct

logical. Only consider direct confounding? Default is FALSE

Value

Logical. Is the variable a confounder?

Details

A confounder is a common cause of x and y. z therefore has to reach x by a directed path that does not run through y, and reach y by a directed path that does not run through x. Being a descendant of z is not enough: descent is transitive through x, so every upstream cause of the exposure, such as an instrument, would qualify even though it opens no backdoor path.

Examples

dag <- dagify(y ~ z, x ~ z)

is_confounder(dag, "z", "x", "y")
#> [1] TRUE
is_confounder(dag, "x", "z", "y")
#> [1] FALSE