Organizations that frequently spend large sums of money on advertising that sells what is not, strictly speaking,  a product or service include political parties,  internal groups,  religious organizations,  and military recruiters. Non-profit organizations are not typical advertising clients, and may rely on free modes of persuasion, such as public service announcements. Advertising spending has increased dramatically in recent years. In 2006, spending on advertising has been estimated at $155 billion in the United States and$385 billion worldwide Advertising is increasingly invading public spaces,  such as schools,  which some critics argue is a form of child exploitation.