AI 中文总结
本研究以卢旺达钨出口为对象，采用Nakano和Nishimura（2025）的识别方法，分四期考察《多德-弗兰克法案》第1502条实施后其价格反应的时间异质性，发现价格反应随时期显著变化。
AI 中文摘要
2010年颁布的《多德-弗兰克法案》第1502条要求，使用来自刚果民主共和国及相邻国家的锡、钽、钨、金（3TG）的美国上市公司，必须披露这些矿产的来源信息。有观点担忧，该监管可能通过规避从受覆盖地区采购，形成事实上的禁运。然而，在制度与市场条件变化下，矿产出口的价格反应如何演变，仍未得到充分理解。由于受覆盖地区的钨生产几乎完全集中在卢旺达，本研究考察2009年1月至2023年12月期间卢旺达钨出口的价格反应。因缺失出口数量数据无法连续观测出口单位价值，本研究采用Nakano和Nishimura（2025）的识别方法，结合联合国商品贸易数据库（UN Comtrade）的月度镜像贸易数据、汇率及世界平均价格。以出口价值为因变量估计进口国固定效应模型，根据制度与市场环境变化将样本分为四个时期。结果显示价格反应存在显著的时间异质性：第1期（η=-20.814，p<0.01）存在统计显著的负向价格反应，第2期（η=1.814，p>0.10）消失，第3期（η=-5.277，p<0.01）再次出现，第4期（η=0.440，p>0.10）又消失。系数差异检验证实，第1期与第2期（p=0.0021）、第3期与第4期（p=0.0006）之间存在显著变化。这些发现表明，卢旺达钨出口的价格反应随时间发生显著变化，并非在监管后呈现统一轨迹。
英文摘要
Section 1502 of the Dodd--Frank Act, enacted in 2010, requires U.S.-listed companies using tin, tantalum, tungsten, and gold (3TG) from the Democratic Republic of the Congo and adjoining countries to disclose information on the minerals' origins. Concerns have been raised that the regulation may have induced a de facto embargo through avoidance of sourcing from the covered region. However, how the price responsiveness of mineral exports evolved under changing institutional and market conditions remains insufficiently understood. Since tungsten production in the covered region is concentrated almost entirely in Rwanda, this study examines the price responsiveness of Rwandan tungsten exports from January 2009 to December 2023. Because missing export quantity data prevent continuous observation of export unit values, we apply the identification approach of Nakano and Nishimura (2025), combining monthly mirror trade data from UN Comtrade with exchange rates and a world average price. An importer fixed-effects model is estimated using export value as the dependent variable, with the sample divided into four periods according to changes in the institutional and market environment. The results reveal substantial temporal variation in price responsiveness. A statistically significant negative price response is observed in Period 1 ($η=-20.814$, $p<0.01$), disappears in Period 2 ($η=1.814$, $p>0.10$), reappears in Period 3 ($η=-5.277$, $p<0.01$), and disappears again in Period 4 ($η=0.440$, $p>0.10$). Coefficient-difference tests confirm significant changes between Periods 1 and 2 ($p=0.0021$) and between Periods 3 and 4 ($p=0.0006$). These findings suggest that the price responsiveness of Rwandan tungsten exports varied substantially over time rather than following a uniform trajectory after the regulation.
