UPDATE 1-"No religion" third world group after Christians, Muslims

* Many have no link to a religion, but may also be spiritual

* Christianity is largest and most widely spread faith

* Islam is second religion, set to grow in future

Dec 18 (Reuters) - People with no religious affiliation make

up the third-largest global group in a new study of the size of

the world's faiths, placing after Christians and Muslims and

just before Hindus.

The study, based on extensive data for the year 2010, also

showed Islam and Hinduism are the faiths mostly likely to expand

in the future while Jews have the weakest growth prospects.

It showed Christianity is the most evenly spread religion,

present in all regions of the world, while Hinduism is the least

global with 94 percent of its population in one country, India.

Overall, 84 percent of the world's inhabitants, which it

estimated at 6.9 billion, identify with a religion, according to

the study entitled "The Global Religious Landscape" issued by

the Pew Forum on Religion and Public Life on Tuesday.

The "unaffiliated" category covers all those who profess no

religion, from atheists and agnostics to people with spiritual

beliefs but no link to any established faith.

"Many of the religiously unaffiliated do hold religious or

spiritual beliefs," the study stressed.

"Belief in God or a higher power is shared by 7 percent of

unaffiliated Chinese adults, 30 percent of unaffiliated French

adults and 68 percent of unaffiliated U.S. adults," it said.

ISLAM EXPANDS

Exact numbers for religious populations are impossible to

obtain and estimates for the size of the larger faiths can vary

by hundreds of millions. This study by the Washington-based Pew

Forum appears to be one of the most extensive to date.

Pew Forum demographer Conrad Hackett said the 2,500

censuses, surveys and population registers used to compile the

report did not allow a further breakdown to estimate the world

population of atheists and agnostics.

"It's not the kind of data that's available for every

country," he said. "A census will typically ask what your

religion is and you can identify a number of particular

affiliations or no religion.

An age breakdown showed Muslims had the lowest median age at

23 years, compared to 28 for the whole world population. The

median age highlights the population bulge at the point where

half the population is above and half below that number.

"Muslims are going to grow as a share of the world's

population and an important part of that is this young age

structure," Hackett said.

By contrast, Judaism, which has 14 million adherents or 0.2

percent of the world population, has the highest median age at

36, meaning its growth prospects are weakest.

Hackett noted that Israel, which has 40.5 percent of the

world Jewish population, had a younger age structure than the

United States, where 41.1 percent of the world's Jews live.

Global Christianity's median age is 30 and Hinduism's 26.

With a median age of 34, the growth prospects for religiously

unaffiliated people are weak, the study showed.

WORLDWIDE BREAKDOWN

The study estimated Christianity was the largest faith at

2.2 billion adherents or 31.5 percent of the world's population.

The Roman Catholic Church makes up 50 percent of that total,

with Protestants -- including Anglicans and non-denominational

churches -- at 37 percent and Orthodox at 12 percent.

There are about 1.6 billion Muslims around the world, or 23

percent of the global population. "The overwhelming majority

(87-90 percent) are Sunnis, about 10-13 percent are Shia

Muslims," the study said.

Among the 1.1 billion unaffiliated people around the world,

over 700 million, or 62 percent of them, live in China alone,

where they make up 52.2 percent of the Chinese population.

Japan comes next with the second largest unaffiliated

population in the world with 72 million, or 57 percent of the

national population. After that comes the United States, 51

million people -- 16.4 percent of all Americans -- said they

have no link to an established faith.

The world's Hindu population is concentrated mostly in

India, Nepal and Bangladesh. Half of the world's Buddhists live

in China, followed far behind by Thailand at 13.2 percent of the

world Buddhist population and Japan with 9.4 percent.

The study found that about 405 million people, or about 6

percent of the world population, followed folk religions such as

those found in Africa and China or among Native American and

Australian aboriginal peoples.

Another 58 million, or nearly 1 percent of the world

population, belonged to "other religions" including Baha'i,

Taoism, Jainism, Shintoism, Sikhism, Tenrikyo, Wicca and

Zoroastrianism. Most were in the Asia-Pacific region.

The study said that 97 percent of the world's Hindus, 87

percent of its Christians and 73 percent of its Muslims lived in

countries where they were a large to overwhelming majority.

Christians make up the majority in 157 countries and Muslims

in 49, including 19 of the 20 states in the Middle East and

North Africa, with the exception of Israel.

By contrast, Hindus are in the majority only in India, Nepal

and Mauritius.

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