Religion Data series: Data Sources and notes
The World Christian Database (WCD) is our main source of data for this series of religion maps. It can be found here: http://worldchristiandatabase.org/wcd/
To quote their website "The World Christian Database provides comprehensive statistical information on world religions, Christian denominations, and people groups." It is maintained by the Center for the Study of Global Christianity at Gordon-Conwell Theological Seminary.
Many thanks are due to Todd Johnson, who cheerfully supplied the answers to many different questions about this data.
We have adjusted the World Christian Database data slightly for two reasons;
We are aware that using the World Christian Database leaves us open to the criticism that we have used a source that may be biased, as a Christian organisation. As the only comprehensive source of religious data by country, there is little choice. However, an academic paper seems to suggest, on the whole, that the WCD generally tallies with data obtained from other sources (Hsu et al., 2006). Another article sums it up as follows (Richard N. Ostling, 2001):
'Barrett' refers to World Christian Database founder David Barrett, also co-author of the World Christian Encyclopedia. Vol. 1 : the world by countries : religionists, churches, ministries.
Data on The Religious Society of Friends (Quakers) has come from the Friends themselves, courtesy of Thecla Geraghty. We have also made occasional use of figures from ARDA, adherents.com and Wikipedia, notably when dividing the Muslim data into Sunni and Shia.
The religions mapped are those used by the World Christian Database. We have also mapped some of the larger and/or more well known Christian denominations, and the two main divisions of Islam.
The data we used is available in Excel and opendocument formats. There is one file (in each format) to cover the whole series. If you need up-to-date religion data, we recommend using our original source - the World Christian Database.
David B. Barrett, George T. Kurian, and Todd M. Johnson, World Christian Encycleopdia: A comparative survey of churches and religions in the modern world, Vol. 1, The world by countries: religionists, churches, ministries (Oxford: Oxford univ. Press, 2001), 120.
Hsu, B., Reynolds, A., Hackett, C. and Gibbons, J. (Forthcoming) "Estimating the Religious Composition of All Nations: An Empirical Assessment." Journal for the Scientific Study (Forthcoming). Pre-publication version available from http://www.princeton.edu/~bhsu/Hsu et al, WCD.pdf
Richard N. Ostling (2001) "Researcher tabulates world's believers", originally published in the Salt Lake Tribune, now available from http://www.adherents.com/misc/WCE.html