Price discrimination is an extremely common type of pricing strategy engaged in by virtually every business with some discretionary pricing power. The issue of whether price discrimination reduces or increases social welfare has been considered by economists since at least 1920. At that time, it was demonstrated that, under certain (restrictive) conditions, price discrimination will reduce social welfare. Subsequent research has shown that price discrimination can increase social welfare, and that a necessary (but not a sufficient) condition for welfare to rise is that total output with discrimination exceeds the no-discrimination level.