International Religious Demography

New Data on World Religions: Introducing the International Religious Demography Project

Todd M. Johnson, Brian J. Grim, and Gina A. Bellofatto

The academic field of religious demography is underdeveloped. Although there are thousands of sources for religious demography, little has been done by scholars in religion, sociology or other disciplines to collect, collate and analyze these. As a consequence, there is much confusion over the status of religion and its adherents around the world. Secondary sources for religious demography, such as, Wikipedia or the CIA Factbook, are woefully inadequate and riddled with errors and contradictions. The World Christian Database (WCD) is the most extensive source, but its focus and methodology have been directed toward measuring Christian adherence.

In 2008, the International Religious Demography (IRD) project was launched for the purpose of providing comprehensive religious demographic information. The IRD project is collecting, collating and analyzing primary and secondary source material on religious demography for all major religions in every country of the world. As data is collected and analyzed, estimates from these sources are made readily available and fully transparent to the scholarly community. The IRD project is currently publishing its findings in an online database (World Religion Database or WRD) and in the future will publish its findings in print.  By offering best estimates based on a methodologically rigorous reconciliation of the various sources’ estimates, the IRD is a valuable resource for anyone doing research on religion.

The IRD project is based at the Institute on Culture, Religion, and World Affairs (CURA) at Boston University. The data primarily come from an analysis of the two largest collections of religious demographic data:

  • The Center for the Study of Global Christianity (CSGC) at Gordon-Conwell Theological Seminary, Hamilton, MA, has over 1 million documents on Christian and religious demography. This Center has detailed information on Christian denominations as well as numerous documents related to other religions. The Center has published much of this data related to Christianity in the World Christian Encyclopedia (Oxford University Press, 2001) and online in the World Christian Database (Brill academic publishers, 2007), but has detailed information on other religions that has not been published.
  • The Pew Forum on Religion & Public Life, a project of the Pew Research Center, in Washington, DC, has collected census, survey and other primary source material on religious demography for many countries and is currently developing detailed adherent estimates for the countries of Africa. The Pew Forum is posting some of this material online, with plans to greatly expand its online religious demographic analysis. Other targeted demographic projects are being planned for the future, including a demographic analysis of the Muslim world in cooperation with Muslim demographers. In time, much of this material will be archived here for scholars and students to use.

The IRD project at CURA provides a venue for the cross-validation of religious demography sources, reconcile conflicting sources of data and determine the best sources for countries where data are in short supply. The project has the capacity to compare cross-tabulated adherent data from demographic and health surveys, census data and other social science sources with other demographic information such as age, level of religious participation, and so forth. However, survey and census data are lacking for many countries of the world. To make estimates for countries where such data is absent, the IRD has the capacity to analyze the CSGC’s unsurpassed collection of religious membership data, as well as draw on its extensive ethno-linguistic data, which provides an alternative method to estimate the size of religious groups in countries for which religious adherent data are not available.

The International Religious Demography project is continually being updated with the latest, most comprehensive and reliable information available. Main directions of the project include conducting cooperative research and publishing the research.


  • Reconcile census and social survey material with clearly sourced data from ethnographic and other data sources to obtain best estimates.
  • Updating a database that allows for past, present and future projections (1900, 1970, 2010, 2025 and 2100) for the 72 major religious affiliation ‘schools’ for the world’s countries (238), provinces (3,000) and cities (5,000).
  • Write methodological notes and articles related to database estimates.
  • Hold colloquia and invite country and demographic experts to provide feedback.

Database Publication

  • The World Religion Database (WRD, is published by Brill as a fee-for-access website designed for researchers and marketed to libraries in the U.S. and abroad.
  • The initial online publication was published in December 2008.
  • The starting points are Oxford University Press’s World Christian Encyclopedia and available country-level census and survey material, with quarterly updates (with the understanding that the WRD is a dynamic and evolving product)
  • The database is structurally similar to the World Christian Database (WCD) where the typical user is someone who knows how to query a database with an option to download the data to an excel file.

Differentiation of the WRD from World Christian Database (WCD)

The WRD is substantively distinct from the WCD, focusing on clearly sourcing estimates of all religions (not primarily Christianity, as is the focus of the WCD) and providing a clear methodology for reconciling differences between religious organization estimates and social scientific estimates. The WRD aims to provide the academic community with the most comprehensive and current information on religious demography on all major religion. .

Feedback on the IRD project

The project plans to provide demographic details on Christian, Muslim, Buddhist, Hindu, Jewish, and other religious traditions and sub-traditions. The information will enable to the user to track changes over time and to observe trends by country and region. The project will also enable users to evaluate claims made by various organizations made about religious demography. Feedback on data and methodology is welcome.

Brief Biographies:

Dr. Johnson is trained as a quantitative historian in the field of ecclesiastical cliometrics—the quantitative analysis of historical data on churches. He specializes in projection methodology for forecasting religious statistics. He is Research Fellow in the Study of Global Christianity at Gordon-Conwell Theological Seminary and a visiting research scholar at the Institute on Culture, Religion, and World Affairs (CURA) at Boston University.

Dr. Grim is trained as a quantitative sociologist and survey methodologist. He specializes in the analysis of cross-national data on religion and on the generation of quantitative data from qualitative sources, particularly in the area of international religious freedom. Grim is a senior research fellow at the Pew Forum. In addition, he is a visiting research scholar at the Institute on Culture, Religion, and World Affairs (CURA) at Boston University as well as he is a research affiliate of the Population Research Institute at the Pennsylvania State University and has recently been a visiting researcher at Georgetown University’s Center for Muslim-Christian Understanding.

Gina BellofattoGina A. Bellofatto is a doctoral student at Boston University’s School of Theology studying the history of sociology, quantitative methods, and international religious demography. Her current demographic projects include the statistics of global Judaism, nonreligious populations, and conversion to and from religion. Her research contributes to the World Religion Database (Brill, 2008), housed at CURA.