Are Trends Stochastic or Deterministic? A Reappraisal of Persistence in Natural Resource Prices
质疑了用线性积分方法分析自然资源价格趋势的适用性，改用更广义的可和性概念，发现价格存在显著持续性，对资源市场预测和政策制定有参考价值。
Whether trends in natural resource prices are stochastic or deterministic is a contentious issue. To resolve this, a number of studies have used the method of integrability to the price series. However, integration is a linear concept. Various studies have suggested that the dynamic path of natural resource prices can be nonlinear, thereby making the choice of integrability methods inappropriate. Using the concept of summability, which is a generalization of integrability, we can appropriately characterize the stochastic properties for a nonlinear process. The results from this analysis find considerable evidence of persistence in natural resource prices..