isCollider {dagitty}

Test for Colliders

Description

Returns TRUE if three given variables form a collider in a given graph.

Usage

isCollider(x, u, v, w)

Arguments

x

the input graph, a DAG.

u

the first endpoint of the putative collider

v

the midpoint of the putative collider

w

the second endpoint of the putative collider

Examples

g1 <- dagitty("dag{X -> Y -> Z}")
stopifnot( isTRUE(!isCollider( g1, "X", "Y", "Z" )) )
g2 <- dagitty("dag{X -> Y <- Z }")
stopifnot( isTRUE(isCollider( g2, "X", "Y", "Z" )) )