In 1995 a committee of Patrick Johnstone (then Editor of Operation World), John Gilbert (then IMB Global Research Office Director), Ron Rowland (SIL / Ethnologue researcher), Frank Jansen (then Adopt-A-People Clearinghouse Director) and Luis Bush (then AD2000 & Beyond Movement Director) decided the Joshua Project definition of “unreached.” The criteria for unreached on the Joshua Project list are:
less than 2% Evangelical --- AND --- less than 5% Christian Adherent
Both conditions must be met to be considered unreached. The terms "Evangelical" and "Christian Adherent" follow the traditional Operation World definitions.
The 5% Adherent criterion was included in the definition of unreached to differentiate between a people group in Afghanistan with 0% Evangelicals and 0% Christian Adherents with no Christian heritage, no access to a Bible, no church, no Christian broadcasts, training, literature, etc. compared to a people group in say Western Europe that may have only a few true Christ-followers but a high number of Christian Adherents with a Christian heritage and access to Bibles, fellowship, broadcasts, training, literature etc. Certainly individuals within these two groups are equally lost, yet one people group is considered unreached while the other would be considered in need of renewal and evangelism. The 5% Christian Adherent criterion helps define the spiritual "environment" (for lack of a better word) of a particular people group.
We cannot avoid the fact that a Christianized people is a very different challenge for evangelism than a non-Christian people.
Patrick Johnstone makes the following observation "We cannot avoid the fact that a Christianized people is a very different challenge for evangelism than a non-Christian people. They may need a personal meeting with Jesus just as much and be equally darkened in their understanding of the Gospel, but you insult them and prejudice your outreach if this is not taken into consideration. Hence my plea that both criteria be retained."
The Joshua Project % Christian Adherent data is people group specific and comes from the following sources: primarily - Operation World supplemental data, Patrick Johnstone, World Christian Database and secondarily - field missionaries and researchers, denominational data and the Ethnologue.