Strategic Modelling and Business Dynamics: A Feedback Systems Approach

3.3. Modelling Symbols in Use: A Closer Look at Drug-related Crime

To see all the modelling symbols in use we revisit the problem of drug-related crime from Chapter 2.^[] Recall the original intention was to identify systemic factors that explain growth in drug-related crime despite the drug busting efforts of police. Figure 3.7 shows the sectors of society involved and one important feedback loop, a reinforcing crime spiral. There are four sectors: the community itself (suffering from crime), the police department (trying to control crime), the street market for drugs and the world of the drug user. A simulatable model of this situation represents the stock accumulations, causal links, information flows and operating policies that lie behind the reinforcing crime spiral. The model is presented sector by sector.

^[] Another way to gain familiarity with the modelling symbols is to work through the iThink tutorial in the CD folder for Chapter 3. You will build a tiny model of population dynamics, develop equations and simulate it. Please bear in mind that you are unable to save the model because the license for the software on the book's CD does not allow newly-built models to be saved. But that doesn't matter in this exercise – the point is to gain familiarity with symbols and conventions of visual modelling in system dynamics.

Figure 3.8 shows the causal links in the community. The community is concerned about drug-related crime and raises its collective concern through a call for ...