Associate Professor, Faculty of Economics, Kyusyu Sangyo University
Visiting Associate Professor, Graduate School of Economics and Management, Tohoku University

Professor, Faculty of Economics, Kansai University
Visiting Professor, Graduate School of Economics and Management, Tohoku University

Professor/Director, Policy Design Lab
Graduate School of Economics and Management, Tohoku University

The interest of this paper is in the area of non-point source pollution, especially that produces a certain large environmental damage in a stochastic manner. Most previous studies on non-point source pollution control policies have implicitly assumed that the abatement efforts of economic agents as a whole can be estimated by assuming environmental damages whose magnitude depends on the abatement efforts of economic agents. When assuming environmental damage that occurs at a certain magnitude in a stochastic manner, the policies proposed by previous studies may achieve efficiency but do not prevent collusion. Therefore, this paper designs new efficiency and collusion-proof policies that work even when not only individual abatement efforts cannot be observed, but furthermore, when the total abatement effort cannot be estimated. Our policy only requires an honest reportig as a whole. By remaining room for adjustment in the reported amount of individual economic agents, our policy is also shown to achieve an equal burden among eocnomic agents.