No single individual's membership perceptibly affects the likelihood that the group will succeed in achieving its goals, yet if it does achieve its goals, every person in the class represented will share in the benefits, regardless of whether he or she was actually a member. The average individual has virtually no incentive to join. Organizations may overcome this problem by supplying services to individual members, in addition to engaging in political activity. The Illinois Farm Bureau and American Association of Retired Persons follow this strategy. Groups such as Common Cause or Ralph Nader's Public Citizen may raise large amounts of money through direct mail.
Interest groups attempt to influence policy by supplying public officials with things they want.
This may include policy information to allow a legislator to take a position on an issue or technical information needed to implement a policy. When the Federal Energy Adn-dnistration was trying to allocate scarce oil and gasoline supplies, it discovered that the information it needed was possessed only by the oil companies. An interest group is most powerful when the issue is narrow and technical and there are no competing interest groups to supply competing information. Finally, it may involve political cues that will allow a public official to line up on the liberal or conservative side of an issue. Although there has been a recent rise in single issue politics, which often generates grass-roots lobbying, members of Congress generally hear what they want to hear and deal with interest groups that agree with them.