Why the differences in unevangelized and unreached population numbers

By Joshua Project’s numbers,there are 3,001,557,000 unreached individuals.
By the Center for the Study of Global Christianity (@CSGC), there are 2,124,216,000 unevangelized individuals.
While these two numbers are “similar” they are different by about 800 million people. Why the difference?
As I’ve noted before, “unreached is not unevangelized.” Part of the difference is in the definition.
A second difference is in how the numbers are computed, and that’s what I’m going to focus on here, briefly.
Joshua Project uses its criteria to identify 7,050 unreached peoples. It totals the populations of each of these groups to arrive at the 3 billion total.
CSGC, on the other hand, calculates the percentage of each group which is Christian, and the percentage of each which is unevangelized. Christians are counted according to affiliated church members of all traditions. The unevangelized are computed by measuring each of 40 ministries (things like the JESUS Film, Scripture distribution, broadcasting, mission work, indigenous church work, etc). Each ministry is estimated to contribute a certain percentage of evangelized; by adding up all the ministries we arrive at a percentage of the population that is evangelized. (And, mathematically, 100 minus this percentage gives us the unevangelized).
So:
CSGC computes the total number of unevangelized individuals as the sum of all the unevangelized individuals within every group. There are some unevangelized people in every group – more in the Punjabi and less among USA Whites, but they are there nonetheless.
Joshua Project only counts the people within the unreached groups – it’s more an “all or nothing” approach. This is entirely appropriate because of the differences in definition. A group is “unreached” in total if the church within the group cannot finish the task without outside assistance.
Now, obviously, the Christians within an “unreached” group are not themselves unreached. But the reality is, they matter very little to the total of Christians or unreached people. Why? Because, for a group to be unreached, the number of Christians must be relatively small (less than 5%).
The net result: numbers that are different (by 800 million) but very similar – almost within a rounding-up of each other. It’s not as if one says 1 billion and the other says 4 billion. And the reason is simple: most groups are either heavily Christian or heavily not, there’s not a lot of groups “in the middle.” Why the difference of 800 million? I haven’t run the numbers in specific, but I’ve got a strong hunch: a lot of the largest unreached groups are heavily evangelized. There’s a lot of work but not a lot of responsiveness (yet!). So while the totality of these groups count toward the unreached populations, less counts toward the unevangelized populations.
What’s the point of all this? Different methodologies can yield somewhat different numbers. Yet, if you understand how and why, you see these two different approaches yield results that are really pretty close to each other. That’s a good check to show the portrait, if fuzzy, is still accurate.
Which number should you use? Use either, but be sure to append the appropriate “unreached” or “unevangelized” when you do. I personally use the unevangelized numbers, but Joshua Project remains my go to website for specific details on specific unreached peoples.