I am new to stats. I am reading the book: Bayesian Networks With Examples in R and already in the first pages, some claims are made which I don't follow.
The author says:
Age and Sex are not influenced by any of the other variables. Therefore, there are no arcs pointing to either variable. On the other hand, both Age and Sex have a direct influence on Education. It is well known, for instance, that the number of people attending universities has increased over the years. As a consequence, younger people are more likely to have a university degree than older people.
His statement doesn't seem to make sense to me... I see it as 'both ways', age depends on education, and education depends on age... Yes, he is right saying that age influences education, if the person is 20 years old is likely to be at undergrad level, but the same goes the other way around if the person has a postdoc, is likely to be > 29 years old...
My question is, is this just a dummy example, with no importance,or am I missing some important theory/aspect?