REPLY Definition of root cause (SD6834)

[SDMAIL Jean-Jacques Laublé]

Posted by  Jean-Jacques Laublé <jean-jacques.lauble at wanadoo.fr>

Hi Bill

You write
<To what degree ought we think of an exogenous parameter as a root cause
<and/or as a high leverage variable, and correspondingly construct models
<based on that?

An exogenous factor can be a root cause of the behaviour of a model, but can
hardly be a leverage point. A high leverage point is a factor that one can influence
in such a way that it will have a great influence on the behaviour of the
model with a minimum of effort. It is by definition endogenous and under control.

But it depends on the definition of a high leverage point.
High leverage point does mean; with a high influence or with a high
influence that is directly or indirectly under control which means that one has the possibility to
change the value of the factor?
For me a leverage point is a high influence factor that one can control.

Root causes can be exogenous or endogenous. If they are endogenous one can
try to influence them directly it they are constants under control.
Otherwise, whether the factor is endogenous out of control or not or
exogenous, the solution is to work with other leverage points to try to find
policies adapted to the influence of that factor.

In the case of the duelling loop that I have not the time to study (sorry
for that), if things are like you depict them, the model has no reasons to
exist and one has no or very little endogenous capability to thwart the
exogenous factors as there is no high endogenous leverage point.
The situation described is like a boat in a storm that has no rudder.

Your comments are then completely justified.
The model is completely contrary to the traditional SD school of thought
that considers mainly purely endogenously driven models. It is there a
nearly pure exogenously driven model.
Regards.
Jean-Jacques Laublé Eurli Allocar
Strasbourg France.
Posted by  Jean-Jacques Laublé <jean-jacques.lauble at wanadoo.fr>
posting date  Tue, 25 Mar 2008 09:38:06 +0100