In Game 4, X represents an individual’s smoking behavior, and Y represents whether the person has asthma as an adult. B represents childhood asthma, which is a collider because it is affected by both A, parental smoking, and C, an underlying (and unobservable) predisposition toward asthma. In Game 5 the variables have the same meanings, but they added two arrows for greater realism. (Game 4 was only meant to introduce the M-graph.)
