Stocks and flows

[jensen568]

Hey, im new to vensim. I cant seem to figure out how to make this stock and flow diagram work..
I would really appreciate som tips/help!

[tomfid]

I think it would be good to start by resolving the unit errors, because some of them suggest conceptual problems in a few equations.

In particular,

Code: Select all

Surveys in execution  = 
        INTEG( ( surveys in executions 
                  + Surveys executed ) 
                  / 2, 
             100) 

I'm not sure what's going on here, but this is integrating the average of the inflow and outflow, both as positive values. Probably this should just be INTEG( surveys in executions - Surveys executed, 100 ). Generally your INTEG expression (i.e. stocks) should only be summing the inflows (added) & outflows (subtracted).

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Cancelled  = 
        Surveys in aqusition 
             * ( 1
                  - 0.8)

Not sure what the "1-0.8" here means, but guessing that this should be made a separate named parameter, like
cancellation rate = 0.2 ~ fraction/year There are several other parameters buried in equations that should be made into separate named variables.

[jensen568]

Thank you for you're reply!