REPLY Structural changes and validity (SD6661)

[SDMAIL Jack Homer]

Posted by  "Jack Homer" <jhomer at comcast.net>

John Gunkler writes:
>I wish there were a better way in SD modeling to show how one policy (rate 
>equation) can become a different one.  We could then have models that 
>adapted to, or learned from, their environments.  While I can think of some 
>workarounds to do this (e.g., embedding an IF-THEN structure in a rate 
>equation), I can't think of ways that maintain the transparency that is the 
>strength of the SD method.

I have heard it said before that SD fails to depict structural change, but 
I've never understood that.  Our models depict behavioral patterns rather 
than individual events, and therefore one should not expect to see discrete 
instances of structural change in an SD model as one might in an agent-based 
model.  But that's OK.  From the behavioral-pattern perspective, a radical 
change in policy(i.e., a structural change), is seen as a shifting in the 
weighting among competing priorities, rather than as the appearance of new 
priorities out of nowhere.  Our behavioral description of this phenomenon is 
"shifting loop dominance".  SD is the only social science methodology that 
maintains a broad, strategic view (avoiding getting lost in the tactical 
details), but still is able to anticipate radical shifts in behavior by 
virtue of the interaction of feedback loops and nonlinearities.

Jack Homer
Posted by  "Jack Homer" <jhomer at comcast.net>
posting date  Sat, 6 Oct 2007 01:04:50 -0400