Reference

The Centers for Disease Control and Prevention is a national public health institute in the United States. It is a United States federal agency, under the Department of Health and Human Services. As the nation's health protection agency, CDC saves lives and protects people from health, safety, and security threats.

The CIA World Factbook is a reference resource produced by the Central Intelligence Agency with almanac-style information about the countries of the world. It provides information on the history, people and society, government, economy, energy, geography, communications, transportation, military, and transnational issues for 267 world entities.

Infoplease is a comprehensive reference source that combines the contents of an encyclopedia, a dictionary, an atlas, and several almanacs loaded with statistics, facts, and historical records. A single search engine allows you to search all these sources at once.

The Library of Congress is the largest library in the world, with millions of books, recordings, photographs, newspapers, maps and manuscripts in its collections. The Library is the main research arm of the U.S. Congress and the home of the U.S. Copyright Office. The Library preserves and provides access to a rich, diverse and enduring source of knowledge to inform, inspire and engage you in your intellectual and creative endeavors.

MedlinePlus is a service of the National Library of Medicine (NLM), the world's largest medical library, which is part of the National Institutes of Health (NIH). The service provides curated consumer health information in English and Spanish with select content in additional languages.

The United States Census Bureau, officially the Bureau of the Census, is a principal agency of the U.S. Federal Statistical System, responsible for producing data about the American people and economy.