R&D is slow magic. It takes many years before research investments begin to affect productivity, but then they can affect productivity for a long time. Many economists get this wrong. Here, we revisit the conceptual foundations for R&D lag models used to represent the temporal links between research investments and impact, review prevalent practice, and document and discuss a range of evidence on R&D lags in agriculture and other industries. Our theory and evidence consistently support the use of longer lags with a different overall lag profile than is typically imposed in studies of industrial R&D and government compilations of R&D knowledge stocks. Many studies systematically fail to recognize the many years of investment and effort typically required to create a new technology and bring it to market and the subsequent years as the technology is diffused and adopted. Consequential distortions in the measures and economic understanding are implied.

中文翻译：

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慢魔法：农业与工业研发滞后模型


R&D是慢魔法。研究投资需要很多年才能开始影响生产力，但随后它们会长期影响生产力。许多经济学家都搞错了。在这里，我们重新审视了用于表示研究投资和影响之间的时间联系的研发滞后模型的概念基础，回顾了普遍的实践，并记录和讨论了农业和其他行业的研发滞后性的一系列证据。我们的理论和证据始终支持使用更长的滞后，其总体滞后特征与工业研发研究和政府研发知识储备的汇编中通常施加的滞后特征不同。许多研究系统性地没有认识到创造一项新技术并将其推向市场通常需要多年的投资和努力，以及随着技术的传播和采用，随后的几年。这暗示了措施和经济理解的间接扭曲。