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Classify DAG nodes

Source: R/classify.R
classify_nodes.Rd

Labels each node as one of: exposure, outcome, confounder, mediator, collider, descendant_of_outcome, or other.

Usage

classify_nodes(dag, exposure, outcome)

Arguments

dag

A dagitty DAG object.

exposure

Optional– inferred from DAG if not set; character; exposure node name (X).

outcome

Optional– inferred from DAG if not set; character; outcome node name (Y).

Value

A data.frame with one row per node and columns:

  • variable (node name)

  • logical flags: is_exposure, is_outcome, is_confounder, is_mediator, is_collider, is_descendant_of_outcome, is_descendant_of_exposure

  • role (a single primary label)

Details

label definitions confounder – ancestor of both X and Y, and not a descendant of X mediator – descendant of X and ancestor of Y collider – node with 2 or more parents on an X / Y path (non-structural) descendant_of_outcome – any descendant of Y exposure / outcome labeled explicitly in function call

Notes:

  • in definitions, x is exposure and y is outcome

  • structural colliders are calculated, but only to define non-structural. structural colliders are not included as a boolean flag

  • A node may satisfy multiple properties; we also return boolean flags for each property. The role column gives a single "primary" label using the precedence defined below.

Examples

  d1 <- dagitty::dagitty("dag { Z -> X; Z -> Y; X -> Y }") # confounder Z
  classify_nodes(d1, exposure = "X", outcome = "Y")
#> variable  role        X  Y  conf  med  col  IO  dMed  dCol
#> X         exposure    x                                   
#> Y         outcome        x                                
#> Z         confounder        x                             

  d2 <- dagitty::dagitty("dag { X -> M -> Y }") # mediator M
  classify_nodes(d2, "X", "Y")
#> variable  role       X  Y  conf  med  col  IO  dMed  dCol
#> X         exposure   x                                   
#> Y         outcome       x                      x         
#> M         mediator               x                       

  d3 <- dagitty::dagitty("dag { X -> C <- Y }") # collider C
  classify_nodes(d3, "X", "Y")
#> variable  role       X  Y  conf  med  col  IO  dMed  dCol
#> X         exposure   x                                   
#> Y         outcome       x                                
#> C         collider                    x    x