Frequently Asked Questions

Click below for answers to some commonly asked questions of CSGC researchers:

Where do you get your numbers?
What’s the fastest-growing religion in the world?
Which is growing faster worldwide, Christianity or Islam?
How do you know what’s going on in North Korea?
Is the United States becoming secularized?
Do you consider Mormons and Jehovah’s Witnesses Christians?
Why do you report such high figures for Christian martyrs?


Where do you get your numbers?

Three major sources for international religious demography are:

  • Censuses where a religion and/or ethnicity question is asked
  • Surveys & polls
  • Data from religious communities

These data are analyzed and reconciled to arrive at the most accurate representation of a country or region’s religious make-up. For a comprehensive overview of the methodology of religious demography, see Todd M. Johnson and Brian J. Grim, The World’s Religions in Figures: An Introduction to International Religious Demography (Malden: Wiley-Blackwell, 2013).


What’s the fastest-growing religion in the world?

Between 2000 and 2010, the fastest-growing religion in the world was Islam, at 1.86% per annum. Over the same period the world’s population grew at 1.20% per annum. See table 1.1 from The World’s Religions in Figures.


Which is growing faster worldwide, Christianity or Islam?

Overall, between 2000 and 2010, Islam grew faster than Christianity. Islam grew at 1.86% per annum, whereas Christianity grew 1.31% (the world’s population grew at 1.20%). In 2010, there were 2.3 billion Christians (32.8% of the world’s population) and 1.6 billion Muslims (22.5% of the world’s population). See table 1.1 from The World’s Religions in Figures.


How do you know what’s going on in North Korea?

It is indeed challenging to assess the religious situation in North Korea, and other similarly closed countries. In difficult cases the CSGC relies on on-the-ground informants for information.

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Is the United States becoming secularized?

Yes and no. The United States has seen a dramatic rise in its nonreligious (atheist and agnostic) population, from just 1.32% of the population in 1900 to 15.1% in 2010. Over the same period, Christians have dropped from 96.4% to 72.0%. However, in terms of raw numbers, Christians are still the vast majority (nearly 250 million in 2010, compared to 44.6 million nonreligious), with great potential for growth due to immigration from the global South (particularly Latin America). The disestablishment of Christianity in the United States early in its history makes the American case quite different from that of Europe.


Do you consider Mormons and Jehovah’s Witnesses Christians?

Like other sociologists of religion, the CSGC utilizes a strict methodology of self-identification. That is, if an individual claims to be Christian, then the CSGC considers him/her a Christian. Mormons and Jehovah’s Witnesses are classified as “North American Independents” in our typology.  This means that they are members of traditions born in the American context as renewal movements within Christianity who self-identify as Christians.


Why do you report such high figures for Christian martyrs?

The CSGC estimates that there have been over 70 million Christians martyred in history. Over half of these were in the 20th century under fascist and communist regimes. In the early 21st century we estimate that on average over the 10-year period from 2000–2010 there were approximately 100,000 Christians killed each year (1 million total). For a detailed explanation of why, please click here.

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Center for the Study of Global Christianity
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