For example, Belgium and other EU countries recommend that policymakers move assertively to decouple economic advancement from growth in material and energy throughput. To improve metrics, policymakers could factor natural capital contributions into economic calculations, and price these to deter degradation or liquidation of natural capital. For example, a healthy and productive forest depends on services provided by nature, incorporating the value of these contributions along with the contributions of labour, fuel, planting, etc., Similarly, impacts that would diminish the productivity or resilience of natural capital could be included along with other costs. Devising additional metrics to measure the impact of the non-obvious and non-quantifiable would provide a useful tool for policymaking. Such measures could include rigorous value and opinion surveys, observational studies of human choices and happiness, alternative assessments of value (such as the value of forests, mountains and coral reefs for tourism and ecosystem services as opposed to just resource extraction), and the like.3.4 SMM policy principle 4.