We introduce time and risk into the fixed-variable cost tradeoff in heterogeneous firm trade models: Investing in exporting gradually and stochastically lowers the costs of exporting. In the model, aggregate trade dynamics arise from producer-level decisions to invest in lowering their future variable export costs, and tariff reforms generate time-varying trade elasticities. The gains from reducing tariffs arise from substituting away from firm creation and towards exporting. This substitution is larger when new exporters are smaller and take longer to grow into successful exporters. The welfare gains from reducing tariffs are much larger than the long-run changes in consumption and the welfare gains cannot be recovered from a static model or from formulas based on those models. Comparing steady-state outcomes can predict a welfare loss from reform when the actual change is positive.

在异构公司贸易模型中，我们将时间和风险引入固定变量成本权衡中：逐步和随机地投资出口降低了出口成本。在该模型中，总的贸易动态来自生产商一级的投资决定，以降低其未来的可变出口成本，而关税改革产生了时变的贸易弹性。降低关税所获得的收益来自于取代企业创立而​​转向出口。当新的出口商规模较小且成长为成功的出口商所需的时间更长时，这种替代方式会更大。降低关税所带来的福利收益远大于长期的消费变化，而且无法从静态模型或基于这些模型的公式中获得福利收益。