Ecosystem-related values are also influenced by the time profile over which they are measured and accounted for. Many of the values of ecosystem services occur over long time scales. Increasingly, the value of ecosystem-related goods and services has become a central issue in environmental policy debates. Further, valuation of ecosystem-related goods and services requires building up a strong and robust evidence base. An important distinction therefore is that economic analysis does not attempt to directly value ecosystem services, but rather assesses the value of the contribution of ecosystem services to related welfare-bearing goods and services. Valuation of ecosystem service related goods can involve a number of complexities; not least of which is that many of these goods are not traded in markets and so lack market prices. Natural science input lies at the heart of any ecosystem service-related valuation. Economics is well-suited to assess the link between quantified ecosystem services and people's well-being.