Public interest groups seek to achieve results that may be enjoyed by the general population. They promote policies that produce widely distributed benefits that anyone can enjoy - for example, clean air or improvements in public health. Unlike a private interest group, if a public interest group achieves its goals, the benefit to any one persons tends to be quite small. Hence, public interest groups tend to rely on numerous small donations and contributions of goods and services to maintain their staffs and programs. As public interest groups have grown and proliferated, the more successful groups have imitated narrower special interest groups to the extent that they can afford to do so, by utilizing specialized professional help from lawyers, consultants, marketers, and lobbyists. But in general, most public interest groups tend to have fewer resources at their disposal than special interest groups.