One of the difficulties in research is estimating the number of Christians in an area (and particularly, for me, estimating the size of a given movement).There are all sorts of reasons why people might want to believe any particular number is too high or too low, or might want to inflate or deflate the number to a particular level. But this doesn’t help us get at the truth. The challenges involved in estimating the size of a movement are the same as those for estimating the size of any large collection of Christians:

- Getting good data - figuring out who to count and how to count them.
- Not letting personal biases or desires get in the way - making sure we don’t inflate/deflate numbers for personal or corporate gain.
- Getting good data, 2 - realizing that there will be some level of error that creeps in, figuring out where the most likely sources of error are, correcting and controlling for those.
- Realizing that data changes - the total number of people is constantly changing. No number will ever be exactly 100% correct - if I said it’s 1,000,000 today, tomorrow it could very possibly be 1,000,001 due to births (or conversions).

Population estimates therefore need to be determined and given in at least one of two ways:

- As a rounded number (such as 1 million, or 100,000, or a 5,500, or the like), with the understanding that the “actual number” is understood to be “within a certain order of magnitude.” Orders of magnitude are usually understand by (a) how people understand rounding or (b) by the number of digits. By estimating a movement at 1 million, it might be somewhere between, say, 900,000 and 1.5 million (or maybe even 2 or 3 million or 700,000) but it’s not 10 million or 100,000.
- As a “range.” This is perhaps better than giving a rounded number, and it’s easier to start with.

To calculate a range, what we need to do for any given movement is try to figure out what the “lower” and “upper” boundary are: the minimum size of a movement, and the maximum. Obviously, if someone’s lying about numbers, the minimum size would be zero: but given sincere workers and believers, that’s likely not the case. The minimum size must therefore be understood to be the lowest possible number it could be given what we understand about the situation and what we understand about the likelihood of error in our counts or methodologies. We also need to think about the highest number it could possibly be, also given what we understand about the situation. The next step of research is to figure out ways to narrow the distance between the upper and lower range. How might we test our methodologies, test for errors, bring greater resolution to the number? Getting an accurate understanding of the situation is essential not just for numbers that we can report. Understanding how big a movement is, how fast it’s growing, where it is weak, where it is strong, are all necessary to knowing where we need to focus our work, and what kind of training and equipping is needed. Athletes training for competitions give great focus to monitoring their performance in order to understand where to work. We should do the same thing with the race that we are running.