Report: Nearly 1 in 4 People Worldwide Is Muslim

The arduous task of determining the Muslim populations in 232 countries and territories involved analyzing census reports, demographic studies and general population surveys, the report says. In cases where the data was a few years old, researchers projected 2009 numbers.

The report also sought to pinpoint the world's Sunni-Shiite breakdown, but difficulties arose because so few countries track sectarian affiliation, said Brian Grim, the project's senior researcher.

As a result, the Shiite numbers are not as precise; the report estimates that Shiites represent between 10 and 13 percent of the Muslim population, in line with or slightly lower than other studies. As much as 80 percent of the world's Shiite population lives in four countries: Iran, Pakistan, India and Iraq.

The report provides further evidence that while the heart of Islam might beat in the Middle East, its greatest numbers lie in Asia: More than 60 percent of the world's Muslims live in Asia.

About 20 percent live in the Middle East and North Africa, 15 percent live in Sub-Saharan Africa, 2.4 percent are in Europe and 0.3 percent are in the Americas. While the Middle East and North Africa have fewer Muslims overall than Asia, the region easily claims the most Muslim-majority countries.

While those population trends are well established, the large numbers of Muslims who live as minorities in countries aren't as scrutinized. The report identified about 317 million Muslims � or one-fifth of the world's Muslim population � living in countries where Islam is not the majority religion.

About three-quarters of Muslims living as minorities are concentrated in five countries: India (161 million), Ethiopia (28 million), China (22 million), Russia (16 million) and Tanzania (13 million).

In several of these countries � from India to Nigeria and China to France � divisions featuring a volatile mix of religion, class and politics have contributed to tension and bloodshed among groups.

The immense size of majority-Hindu India is underscored by the fact that it boasts the third-largest Muslim population of any nation � yet Muslims account for just 13 percent of India's population.

"Most people think of the Muslim world being Muslims living mostly in Muslim-majority countries," Grim said. "But with India ... that sort of turns that on its head a bit."

Among the report's other highlights:

_ Two-thirds of all Muslims live in 10 countries. Six are in Asia (Indonesia, Pakistan, India, Bangladesh, Iran and Turkey), three are in North Africa (Egypt, Algeria and Morocco) and one is in sub-Saharan Africa (Nigeria).

_ Indonesia, which has a tradition of a more tolerant Islam, has the world's largest Muslim population (203 million, or 13 percent of the world's total). Religious extremists have been involved in several high-profile bombings there in recent years.

_ In China, the highest concentrations of Muslims were in western provinces. The country experienced its worst outbreak of ethnic violence in decades when rioting broke out this summer between minority Muslim Uighurs and majority Han Chinese.

_ Europe is home to about 38 million Muslims, or about five percent of its population. Germany appears to have more than 4 million Muslims � almost as many as North and South America combined. In France, where tensions have run high over an influx of Muslim immigrant laborers, the overall numbers were lower but a larger percentage of the population is Muslim.

_ Of roughly 4.6 million Muslims in the Americas, more than half live in the United States although they only make up 0.8 percent of the population there. About 700,000 people in Canada are Muslim, or about 2 percent of the total population.

A future Pew Forum project, scheduled to be released in 2010, will build on the report's data to estimate growth rates among Muslim populations and project future trends.

A similar study on global Christianity is planned to begin next year.