Football pick scams - the inverted pyramid by Wikipedia

"In the football picks scam the scammer sends out tip sheet stating a game will go one way to 100 potential victims and the other way to another 100. The next week, the 100 or so who received the correct answer are divided into two groups and fed another pick. This is repeated until a small population have (apparently) received a series of supernaturally perfect picks, then the final pick is offered for sale. Despite being well-known (it was even described completely on an episode of The Simpsons and used by Derren Brown in "The System"), this scam is run almost continuously in different forms by different operators. In Rex Stout's Novel And Be a Villain (1948) this horse race prediction scheme is described by Nero Wolfe as a sure way to make money if one was so inclined to commit a crime. The sports picks can also be replaced with securities, or any other random process, in an alternative form. This scam has also been called the inverted pyramid scheme, because of the steadily decreasing population of victims at each stage."