In a model with moral hazard and asymmetric information, we show that it can be welfare improving to differentiate patent lives when firms have different R&D productivities. A uniform patent life provides too much R&D incentive to low-productivity firms and too little to high-productivity ones....

This paper is an empirical study of what motivates individuals to donate to a charity. It is based on a unique dataset from the English National Opera (ENO) which includes detailed information on attendance and both granted and actually consumed bene ts by all donors. We nd that individuals...