I've been doing some number-crunching about how many Slayers there are in the Buffyverse. The headline figures are as shown below, the assumptions and hypotheses I made to arrive at the conclusions are under the cut. None of these numbers are set in stone - I had to make some fairly random guesses on some of the data - but they feel in the right ballpark to me. Feel free to challenge any of my assumptions!
- Every year, approximately 500 new Potential Slayers are born.
- One baby in 260,000 is a Potential (or one girl baby in 130,000). Put another way, if you're pregnant, you have a 0.000385 % chance of giving birth to a Potential Slayer.
- One Potential is born each year for every 13.4 million people. Four or five per year are born in Britain; about 23 in the US.
- After 'Chosen' there is one Slayer for every 2.7 million people, because several generations were Called at once due to Willow's spell. An extra Slayer per 13.4 million people will be added each year thereafter as a Potential reaches the appropriate age, unless pogroms or Twilight intervene. Or to put it more clearly:
- In Britain, with a population of 60 million, there are 22 Slayers plus another five per year.
- In the US with a population of 307 million, there are 114 Slayers plus an extra 23 per year.
- At the start of Season 7, there were 10,000 Potentials under the age of 20. Of these, 3,000 were old enough to become Slayers while the other 7,000 were still too young.
- The Watchers' Council knew of 1,600 of these Potentials, including 500 of the right age to be Called as Slayers. 95% of these 500 Council-trained teenage Potentials were murdered by The First's minions, leaving around 25 to escape to Sunnydale.
- That left around 2,500 Potentials who were made into Slayers in 'Chosen', of whom 80% have been tracked down by Buffy and Willow and their team. Almost all of these Potentials were never identified by the Council - which, I assume, is why the First never found them either.
- In its heyday the Council had nearly 1,300 Watchers out in the field around the world, not counting headquarters staff and special projects teams.
In 'The Long Way Home', we get one piece of solid data: there are now 1800 Slayers "that we've counted". Later issues of the comic up this figure to "just under 2,000"; this may be simple rounding or because new Slayers continue to be discovered over the course of the early season.
While not completely confirmed by canon, it's strongly implied that only girls in their mid-to-late teens are eligible to become Slayers, with a few outlying exceptions here and there. Buffy was 15, Faith was 17, Kennedy thinks that at 19 she's getting too old. In 'Harmonic Divergence' we see a girl getting Called on her 16th birthday. I'm going to take it as a hypothesis, then, that in general Potentials can become Slayers between the ages of 14/15 and 19/20, a six-year time window.
We now have to make an assumption: how many unknown Slayers are still out there, not yet contacted by Buffy and her team? We have no data so can only guess. However, I assume that they would have been using mystical means to track down the Slayers so should have a reasonably good idea how many there are. Therefore, Buffy's figures might be out by a few hundred, but not by an order of magnitude. As such, my hypothesis is that the "nearly 2,000" figure accounts for about 75-80% of all the Slayers out there.
The second assumption we have to make is how many Potentials were murdered by The First's minions during Season 7. The only data we have here is that Giles was able to rescue about 25 - 30 girls and bring them to Sunnydale, and he refers to this number as "just a handful" compared to how many there used to be. At this point, we have to pull figures out of the air: but if we assume that "a handful" means about 5%, then before The First began Its massacre there would have been around 600 Potentials of the right age known to the Council. (5% of 600 is 30, the high-end figure for the number of rescued Potentials.) If "a handful" means 10%, then there were 300 teenage Potentials being supervised by the Council. Call it 500 in round numbers.
Giles didn't rescue any child Potentials, only teenagers. Either he didn't think they were in danger or he was unable to save any of them because they were too vulnerable. Another assumption I'm making, then, is that he rescued only "a handful" of the teenage Potentials, rather than saving most of them but leaving all the kiddies to die...
Therefore, putting those figures together, we can say in round numbers that there would have been about 3,000 Potentials of the right age to become Slayers at the beginning of Season 7. If we assume The First killed around 500 of them, that leaves around 2,500 Slayers to be Called by the spell in Chosen, almost all of whom were presumably unknown and undetected by the Council beforehand. Buffy and her friends have accounted for nearly 2,000 of these, leaving about 500 still operating off the radar or going about their lives.
As I said, there's a fair bit of guesswork involved in those numbers, but they feel in the right ballpark to me.
We can therefore start making some calculations.
If there were 3,000 Potentials between the ages of 14 and 19, assuming they're evenly spread in ages that makes 500 who were 14, 500 who were 15, and so on - in other words, this is where I get the figure of 500 new Potentials being born each year.
If the Council had records of about 500 of those 3,000 Potentials, that makes only one in six. However, one hypothesis would be that the chance of each Potential becoming the Slayer is not purely random, rather that some girls have better odds than others - and if the divination magic or whatever the Watchers use to track down Potentials detects that, it could mean that they were able to train and control a much higher percentage of Slayers than the one-in-six figure would otherwise indicate.
As a datapoint, of the three Slayers we see before the final season, only Kendra had a Watcher since childhood. Buffy was discovered by Merrick after she became a Slayer, and Faith really doesn't give the impression of someone who was brought up under the tutelage of a Watcher either. Based on that, my speculation is that around a third of Slayers are Watcher-trained (double the number the raw figures would suggest), while the rest are only tracked down soon after they become Slayers. (A few might never get discovered at all: I suspect that was much more likely in the days before mass communication and international travel, though.)
If 500 Potentials are born per year, that makes 10,000 of them below the age of 20. Applying the one-sixth proportion means that the Council was aware of 1600 of them; if we further assume that they normally assigned Watchers when the children reached the age of five, that gives us the figure of approximately 1300 Field Watchers throughout the world.
At some point I might write more about how I think the Council was organised, but that's for another day.
Questions? Comments? The part that's less fun, when there's no screaming?