People are often interested in statistics concerning how many people in the world are Christian, how many actually go to church, how many Christians are Catholic, and so on. Unfortunately, it is very difficult to get any sort of really accurate information on such topics, whether involving Christianity or any other religion.
Ideally, Christianity should be among the easiest religions to get data on because unlike many other religions, there is an effort to keep statistical records when it comes to baptisms, church attendance, etc. The reality, however, is quite different - for example, the Roman Catholic Church officially records as members everyone who was baptized a Catholic, whether they still want it that way or not. To what extend should independent observers accept those numbers as genuinely accurate?
Perhaps we could try surveys in order to get a better idea of where people belong, but they can be even less accurate. Many adults will fill out forms indicating membership in a church that they haven't attended in decades. Why? Because they grew up in that church and because their family were always members, so they still consider themselves members - for them, "membership" in a Christian church doesn't require regular attendance or devout acceptance of its doctrines.
Then there is the well-known phenomenon that people often report on surveys what they think that others want to hear. When some activity or group is looked down upon in society, it is very difficult to get people to admit to such activity or membership even on anonymous surveys. Atheism is, obviously, harshly criticized in many sectors of American society, not to mention other cultures around the world, so we can expect that not everyone who is an atheist will necessarily admit to it.
Still, the fact that we can't have completely reliable numbers doesn't mean that we don't have any numbers at all. It does, however, mean that we must treat the numbers with a great deal of caution. To that end, I have included here numbers from more than one source. They don't all agree, but they do provide a general idea about the state of Christianity in the world.
Source: 1997 Britannica Book of the Year. © 1997 Encyclopædia Britannica, Inc.
- Total Religious Population: 5,804,120,000
Christians (total): 1,955,229,000 (33.7%)
Roman Catholics: 981,465,000 (16.9%)
Protestants : 404,020,000 (7.0%)
Orthodox: 218,350,000 (3.8%)
Anglicans: 69,136,000 (1.2%)
Other Christians; 282,258,000 (4.9%)
Source: International Bulletin of Missionary Research, January 2003. David B. Barrett & Todd M. Johnson.
- Christians (total): 2,076,629,000 (33.1%)
Roman Catholics: 1,097,144,000
- Catholic Church: 1,050,000,000
Orthodox Churches: 270,000,000
Anglican Communion: 73,000,000
Assemblies of God: 32,000,000
Jehovah's Witnesses: 15,374,986
Southern Baptist Convention: 15,000,000
Church of Jesus Christ of Latter-day Saints: 11,721,548
United Methodist Church: 11,708,887
Seventh-day Adventist Church: 11,300,000
Evangelical Lutheran Church in America: 5,500,000
United Church of Canada: 3,000,000
Presbyterian Church (U.S.A.): 2,560,201
Churches of Christ: 2,000,000
Syrian Orthodox Church ("Jacobite"): 2,000,000
Salvation Army: 1,500,000
American Baptist Churches in the U.S.A.: 1,455,855
United Church of Christ: 1,377,320