Suppose firms are subject to decreasing returns and permanent idiosyncratic productivity shocks. Suppose also firms can only stay in business by continuously paying a fixed cost. New firms can enter. Firms with a history of relatively good productivity shocks tend to survive and others are...

Recent empirical studies suggest a need for a ?exible patent regime responding to industry characteristics. In practice, sector-speci?c modi?cations of patent strength already exist but lack theoretical foundation. This paper intends to make up for this neglect by scrutinizing in what direction...