We extended the QSSI to accommodate flows of different strength by assigning a value to the flows ranging from 1 = weak to 3 = strong. The weights of the flows can be deduced from stakeholder participation, expert judgments, and empirical evidence. Figure 11.3 illustrates this.
With weights assigned, the QSSI is calculated as the sum of the weights of the inconsistencies divided by the sum of weights of all flows. In our example, the QSSI is 18/47 = .38. Solving a strong inconsistent flow has a larger impact on the QSSI than removing a weak flow. The QSSI is .33 when a strong inconsistency is removed and .36 when a weak inconsistency is removed. With weights added, possible interventions can also be aimed at the strength of flows, giving room for issues such as eco-efficiency and technological progress that push the frontiers of sustainability without fundamentally changing the system.
In addition, weighted flows and inconsistencies provide arguments to reject inconsistencies based on their significance. If a stock is strongly consistent with one and weakly inconsistent with another stock, then the weak inconsistency is of low priority when it comes to action for sustainability unless the inconsistency itself is highly undesirable. The weighted QSSI implicitly takes this into account. It requires a high con-
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