Communication by Interest Groups and The Organization of Lobbying1

This Version Abstract: This paper uses a mechanism design approach to characterize the opti-mal organization of lobbying groups in a political context where those groups have private information on their ideal points in a one-dimensional policy space. First, we derive the optimal mechanism for one single group and show that it depends on the conflict of interests between his own preferences and those of the policy-maker but also on how informative the distribution of the interest group’s ideal point is. We then extend the analysis to the case of multiple interest groups. Although deal-ing with a coalition of those groups allows the policy-maker to benefit from a more precise information (an informativeness effect), the optimal organization may nev-ertheless call for a decentralized mechanism where groups compete because this is the only way to transmit information on the relative strength of their preferences (a screening effect). A coalition of interest groups dominates for small values of the conflict of interests whereas competing interest groups emerge for greater values