Section 19 The shared arrow rule, functional form.
When joining two causal maps containing one shared influence variable C and one shared consequence variable E, the first encoding an influence \(f\), and the other encoding an influence \(g\), the combined influence can be calculated in the same way as in the [previous section][#shared-influence-function].
An example of contradictory maps:
If we hear
heart disease increases strongly with alcohol consumption
and
..In the absence of any other information, we perhaps suggest some kind of average influence. The situation seems simpler when the information is not contradictory:heart disease is hardly affected by alcohol consumption
If we hear:
heart disease increases strongly with alcohol consumption
and
heart disease increases strongly with alcohol consumption
… we are usually only too happy to combine the mini-maps. The combined function can be calculated as in the previous section.