In many countries hospital regulation undergoes fundamental change. In reaction to steadily increasing costs, authorities switch from cost of service regulation to prospective payment systems (PPS). While it seems clear that this new scheme sets strong cost saving incentives, this is not so...

We extend the models in ("Competition in two-sided markets" of Armstrong (2006, Rand Journal of Economics) by adding within-group externalities. In the monopoly and duopoly cases, positive within-group externalities reduce the price of the own group. Negative externalities have an opposite price...