Activate paths opened by stratifying on a collider

Stratifying on colliders can open biasing pathways between variables. activate_collider_paths activates any such pathways given a variable or set of variables to adjust for and adds them to the tidy_dagitty. A pathway is added for a pair of variables upstream of an adjusted collider only when the adjustment opens a path between them that is closed without it, so variables joined only by a path that the adjustment leaves as it found it are not connected. Openness is judged under the whole of adjust_for, so adjusting for a collider and for a variable that blocks the path it opens leaves the pair unconnected.

Usage

activate_collider_paths(.tdy_dag, adjust_for, ...)

Arguments

.tdy_dag

A tidy_dagitty or dagitty object

adjust_for

a character vector, the variable(s) to adjust for.

...

additional arguments passed to tidy_dagitty(). These are only used when .tdy_dag is not already a tidy_dagitty.

Value

a tidy_dagitty with additional rows for collider-activated pathways

See also

control_for(), ggdag_adjust(), geom_dag_collider_edges()

Examples

dag <- dagify(m ~ x + y, x ~ y)

collided_dag <- activate_collider_paths(dag, adjust_for = "m")
collided_dag
#> # DAG:
#> # A `dagitty` DAG with: 3 nodes and 3 edges
#> # Paths opened by conditioning on a collider: x <-> y
#> #
#> # Data:
#> # A tibble: 5 × 8
#>   name          x      y direction to         xend   yend collider_line
#>   <chr>     <dbl>  <dbl> <fct>     <chr>     <dbl>  <dbl> <lgl>        
#> 1 m     -5.02e- 1 -0.290 NA        NA    NA        NA     FALSE        
#> 2 x      5.02e- 1 -0.290 ->        m     -5.02e- 1 -0.290 FALSE        
#> 3 y      1.15e-10  0.579 ->        m     -5.02e- 1 -0.290 FALSE        
#> 4 y      1.15e-10  0.579 ->        x      5.02e- 1 -0.290 FALSE        
#> 5 x      5.02e- 1 -0.290 <->       y      1.15e-10  0.579 TRUE         
#> #
#> # ℹ Use `pull_dag() (`?pull_dag`)` to retrieve the DAG object and `pull_dag_data() (`?pull_dag_data`)` for the data frame