双重差分模型在政策环境评价中的应用研究——以农业支持保护补贴政策为例

Application of difference-in-differences model in policy-based strategic environmental assessment: taking policy for agricultural support and protection subsidy as an example

政策环境评价是环境影响评价体系的重要组成部分,开展其方法研究对政策环境评价制度完善及实践开展至关重要。双重差分(DID)是计量领域用于政策效果评估的主流方法之一,以农业支持保护补贴政策为例,采用多期DID评估该政策对农业面源污染的影响,探究DID在政策环境评价中的适用性。结果表明,DID在政策环境评价中具有较好的适用性,可用于政策实施后的环境影响评价和政策实施前相关政策的回顾性评价。未来应加强政策环境评价的技术方法研究,形成统一完善的技术方法体系,以促进政策环境评价制度的构建与实践的开展。研究发现,政策设计上环境利好的农业支持保护补贴政策在研究区域对农业面源控制的正向影响并不显著,甚至刺激农户施用更多农药,产生了负面影响。

Policy-based strategic environmental assessment(policy-based SEA) is an important part of the environmental impact assessment system. It is very important to carry out the method research of policy-based SEA for its system improvement and practice. Difference-in-differences(DID) is one of the main methods used to evaluate policy effects in econometrics. Taking the policy of agricultural support and protection subsidy as an example, multi-period DID was used to evaluate the impact of the policy on agricultural non-point source pollution,and explore the applicability of DID in policy-based SEA. This study found that DID had good applicability in policy-based SEA. In addition to the environmental impact assessment of post-implementation policies, DID could also be used for the retrospective evaluation of the relevant policies of pre-implementation policies. In the future, the research on technical methods of policy-based SEA should be strengthened, and a unified technical method system should be formed to promote the construction and improvement of policy-based SEA system. In addition, it was found that although the policy for agricultural support and protection subsidy was a favorable policy for environment, its positive impact on agricultural non-point source pollution was not significant, and even stimulated farmers to use more pesticides, resulting in a negative environmental impact.