"Christians comprise nearly 80 percent of the U.S. population."...AP, (2nd to last parag.)
Dec. 19, 2011, "Global Christianity, " Pew forum on Religious and Public Life, Executive Summary
"There are 2.18 billion Christians of all ages around the world, representing nearly a third of the estimated 2010 global population of 6.9 billion....Christians are by far the world’s largest religious group. Muslims, the second-largest group, make up a little less than a quarter of the world’s population, according to previous studies by the Pew Forum.3 ....Footnotes: 3. As of 2010, there were about 1.6 billion Muslims worldwide, representing 23.4% of the global population....
These are some of the key findings of Global Christianity: A Report on the Size and Distribution of the World’s Christian Population, a new study by the Pew Research Center’s Forum on Religion & Public Life.
The study is based primarily on a country-by-country analysis of about 2,400 data sources, including censuses and nationally representative population surveys. For some countries, such as China, the Pew Forum’s estimates also take into account statistics from church groups, government reports and other sources. (See Appendix C [PDF] for more details on the range of estimates available for China.) ...
12/19/11, "Study: Christian population shifts from Europe," AP. R. Zoll