The literature on R&D-based growth establishes that market equilibrium is inefficient and derives optimal R&D policy. Normative analyses of this type use the assumption of steady state, largely motivated by analytical convenience. This paper questions this steady-state approach by introducing endogenous cycles as long-run equilibria. We show that the government fails to maximize welfare if policy which is optimal in steady state is myopically applied in cyclical equilibria. More specifically, we demonstrate that (ⅰ) cycles arise in the (very) standard R&D-based model of Grossman and Helpman [1991. Innovation and Growth in the Global Economy. MIT Press, Cambridge, MA (Chapter 3)] once the model is framed in discrete time, (ⅱ) these cycles are inefficient in the sense that they prevent welfare maximization, (ⅲ) optimal steady-state R&D policy fails to eliminate cycles, and can even create inefficient cycles, (ⅳ) the application of R&D subsidies leads to a trade-off between growth and macroeconomic stability, and (ⅴ) optimal R&D policy in a fluctuating economy is state-dependent, which generalizes optimal steady-state R&D policy.
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机译：基于R＆D的增长的文献确定市场均衡是无效的，并得出了最佳的R＆D政策。这种类型的规范分析使用稳态假设，这主要是出于分析便利性的考虑。本文通过引入内生循环作为长期平衡来质疑这种稳态方法。我们证明，如果将近稳态下最优的政策近观地应用于周期性均衡中，政府将无法实现福利最大化。更具体地说，我们证明了（ⅰ）周期出现在Grossman and Helpman [1991]的（非常）基于标准R＆D的模型中。全球经济中的创新与增长。麻省理工学院剑桥分校的麻省理工学院出版社，马萨诸塞州剑桥市（第3章）]，一旦模型在离散时间内构建，（ⅱ）这些周期在防止福利最大化方面就显得无效，（ⅲ）最佳稳态研发政策无法消除周期，甚至会造成效率低下的循环，（ⅳ）应用研发补贴会导致增长与宏观经济稳定之间的权衡，（ⅴ）波动经济中的最佳R＆D政策取决于国家，从而概括了最佳稳态R＆D政策。
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