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Basic Variable needed for system dynamics models:

 

Stocks

Flows

Auxiliary Variables

 

Data Variables

 

Data variables represent time series information.  These may represent historical data, but they may also be used to  represent forecasts or plans.  Data variables may be compared to model results in order to validate or calibrate a model.  They are also used as exogenous inputs or plans that drive model behavior.

 

Aggregate Variables

 

Aggregate variables represent values calculated from all the values of a specific entity variable from all members of a collection or sub-collection.  The most common of these