In the early 1990s, the Southern Baptist Church of Alabama produced the first mathematics-driven estimates of how many people are going to hell.

The estimates were a practical tool, a guide for where to concentrate the church's evangelical efforts and where not to bother. Any well-run modern business does this. A company that sells insurance or cereal or cars likes to let its sales force know how many dependable customers are in each region, how many potential new customers, and also how many marginal prospects - people not worth wasting time on. With this information, the sales force can focus its efforts productively. So it is with the Southern Baptist Church of Alabama.

The church assumes that in a given neighbourhood, nearly all the Southern Baptists are already saved (they also assume that, people being people, a certain small percentage are damned idiots). Other Baptist and evangelical denominations are a mixed lot - some are still savable, others have irrevocably blown it. Most, but not all, Catholics are a lost cause. Non-Christians - Jews, Muslims, Hindus, Confucians, atheists and others who refuse to accept Jesus - can be written off, evangelically speaking.

The Southern Baptist Convention's Home Mission Board did all the work on this. It devised a secret mathematical formula, estimating what percentage of each religious group will go to hell: X% of Southern Baptists, Y% of Episcopalians, Z% of Catholics, and so on. The Home Mission Board puts great faith in these percentages.

It was easy to find out how many people of each faith live in each Alabama county. A group called the Glenmary Home Missioners Board, in Ohio, periodically publishes a massive county-by-county survey of the entire US. The Southern Baptist Convention fed the 1990 survey numbers into its formula. The numbers that popped out are collectively called the evangelistic index.

The evangelistic index was not meant to be celebrated. Like any sales estimate, it was prepared for the organisation's internal use. But someone gave parts of it to Greg Garrison, a reporter for the Birmingham News, and the newspaper published a page one article revealing that: "More than 1.86 million people in Alabama, 46.1% of the state's population, will be damned to hell if they don't have a born-again experience professing Jesus Christ as their savior, according to a report by Southern Baptist researchers."

The Birmingham News suggested this was just the half of it. But, actually, this was just the 1/50th of it. The Southern Baptist Church of Alabama made estimates of how many people are going to hell in every county in all 50 of the American states. The countrywide figures have never been made public. But using the Alabama data as a guide, anyone can calculate the algorithm that produced them. And once you have that, you can apply it to population figures for the other 49 American states - and to almost any region of any country on earth. Then you'll know, at least in theory, who's going to be hot and who's not.

· Marc Abrahams is the editor of the bimonthly Annals of Improbably Research and organiser of the Ig Nobel prize