> But then he uses the model wrongly, since he puts "hidden factor" "smoking" "lung cancer" in the vertices, and not "hidden factor (t=0)", "smoking(t=1)" and "

> But then he uses the model wrongly, since he puts "hidden factor" "smoking" "lung cancer" in the vertices, and not "hidden factor (t=0)", "smoking(t=1)" and "lung cancer(t=2)". The direction of the arrows shows causation with also implies time has passed though the amount of time is not specified in the model he is using, though it could be added. He has a section latter in the article about why he left it absent earlier and covers how it could be included. > Further if used like that, then a possible hidden factor could actually be "lung cancer(t=0)", since it could (conceivably) cause both "smoking(t=1)" and "lung cancer(t=2)". If lung cancer actually caused smoking then yes that would a simple solution. If that was the answer though the very next question would be what caused "lung cancer(t=0)". Which "smoking(t=-1)" if existed would be suspect, and another "hidden factor"(s) of course as well.