Lobbying For Legislators’ Vote

How do lobbyists for special interest groups decide on the right amount of money to spend to influence the votes of legislators? Research by Michel Le Breton and Vera Zaporozhets analyses the key components of the political process for the two sides on big adversarial issues, such as abortion, gun control, whether an industry should be liberalised and whether an international agreement should be ratified.

Their study, published in the March 2010 Economic Journal, calculates a single summary statistic that makes it possible to predict the minimal budget that a pro-reform lobby needs to invest to win the political competition against a pro-status quo lobby. Key driver of this are the relative strengths – or 'degree of asymmetry' – between the two competing interest groups, and legislators' openness to manipulation.

The main goal of democratic institutions is to give voice to different interests of society in the decision-making process. So it is not surprising that particular interest groups may try to influence their representatives' votes to gain advantage. One way of doing that is by contributing money to politicians in exchange for their votes.

Concern about the influence of money on political decisions is not new, and it is the object of widespread criticism of the political systems in many countries. To make legislative institutions more resistant to the influence of special interest groups, contributions are often regulated and limited by law.

For example, even though in the United States, campaigning is an essential part of the electoral process, in the House of Representatives, a stringent code of ethics restricts outside income to a total of 15% of a member's salary, limits honoraria to $1,000, etc.

A crucial point for efficient regulation is to understand how special interest groups interact and how they consequently allocate campaign funds among the various legislators, bureaucrats and decision-makers to achieve their aims efficiently.

To explore these questions, this study analyses a situation in which two lobbies compete to influence the votes of a group of legislators voting on two alternatives. Many policy issues fit that formulation, for example, whether or not an industry should be liberalised, whether or not an international agreement should be ratified, whether or not the free sale of guns should be banned, and whether or not abortion should be allowed.

The researchers calculate the amount of money that has been invested in the political process as well as its distribution among legislators. Special attention is paid to three key components of the political environment:

  • the internal organisation of the legislature;
  • the degree of asymmetry between the lobbies;
  • and the proportion of 'bad' and 'good' legislators in the political arena.

The first contribution of this research consists of identifying the conditions under which the pro-reform lobby will make positive offers to some legislators. The researchers show that if there is too strong an asymmetry between the lobbies, the pro-status quo lobby will abandon the prospect of influencing the legislature as it will be rationally anticipating its defeat. In fact, it will make offers only if it is certain of success.

The minimal amount of asymmetry – the 'victory threshold' – defines how much the pro-reform lobby's stake must outweigh the pro-status quo lobby's stake to make sure that the pro-reform lobby wins. The study illustrates the calculation of the victory threshold and shows that it is closely related to concepts from cooperative game theory.

When the legislators are concerned only about monetary contributions, the victory threshold only depends on the decision rules operating in the legislature. It corresponds to what other researchers (Diermeier and Myerson, 1999) have called the hurdle factor of the legislature.

This single parameter acts as a summary statistic making it possible to predict the minimal budget that the pro-reform lobby needs to invest to win the competition. This number can be also considered as a measure of the legislature's vulnerability to manipulation.

Another important issue is to understand how the lobbying budget will be allocated across legislators. As legislators differ in two respects – the intensity of their preference for a reform and their position/power in the legislature – the price of a legislator's vote is likely to be a function of both parameters. The researchers illustrate the calculation of these prices in some important real world decision-making bodies.

'Sequential Legislative Lobbying Under Political Uncertainty' by Michel Le Breton and Vera Zaporozhets is published in the March 2010 issue of the Economic Journal. Michel Le Breton and Vera Zaporozhets are at the Toulouse School of Economics