[1.1] dag: training <- ability -> wages

[1.2] confounders: ability; colliders: none; mediators: none

[1.3] condition on ability to block its confounding effect

[2.1] dag: training -> productivity -> wages

[2.2] confounders: none; colliders: none; mediators: productivity

[2.3] for total effect: do not condition on productivity; for direct effect: condition on productivity

[3.1] dag: training -> included <- wages

[3.2] confounders: none; colliders: included; mediators: none

[3.3] do not condition on included (and do not restrict to included==1)