The welfare cost of one-size-fits-all patent protection

To analyze the welfare gain from allowing for differentiated patent protection across sectors, this study develops a two-sector quality-ladder growth model in which patent breadth is a policy variable and derives optimal patent breadth under two patent regimes. We show that (a) uniform optimal patent breadth is a weighted average of sector-specific optimal patent breadth and (b) sector-specific optimal patent breadth is larger in the sector that has a larger market size and more technological opportunities. To derive the optimal policy, we allow for an arbitrary path of patent breadth and derive the optimal path by solving a Stackelberg differential game. We find that the optimal path of patent breadth under each patent regime is stationary, time-consistent and subgame perfect. Finally, we perform a numerical investigation and find that even a moderate degree of asymmetry across sectors can generate a significant welfare cost of uniform patent protection.