REPLY Meaning of Stock/Level (SD6937)

[SDMAIL Ingram,Allan E - PFR-6]

Posted by  "Ingram,Allan E - PFR-6" <aeingram1 at bpa.gov>

The example of ratios describing customer preference for new vehicles 
presented by Jean-Jacques Laublé’ appeals to me. His modeling allows 
examination of his business with varying degrees of new vehicle 
preference. Formal or informal customer surveys provide the objective 
basis for establishing the business impact of customer preference. This 
approach creates a clear connection between customer preference and 
business performance that invites regular updates from experience.

I view subjective variables as best modeled by dimensionless weighting 
factors affecting efficiency or performance variables or by modifying 
delays in information flows. I am uncomfortable creating subjective 
stocks with units that influence physical or financial flows.

My discomfort is focused on the impact of subjective variables within 
the structure of SD models.  SD modeling  provides structures that help 
us understand how pre-existing mental models lead us astray. For me, 
whenever exogenously subjective stocks are put in a stock/flow 
structure, they are  likely to impose an unverified mental model. Are 
there suggestions regarding how to verify a purely subjective stock with 
observations or experience? What would a model of  truck rental income 
per day with an input flow measured in Trust/customer look like?

Posted by  "Ingram,Allan E - PFR-6" <aeingram1 at bpa.gov>
posting date  Fri, 18 Apr 2008 16:49:39 -0700