Congratulations to the US Women's National Team, which is in the Women's World Cup final thanks to Cari Lloyd, Kelley O'Hara... and statistics.
Like many sporting events, the Women's World Cup is, in these later stages, a single-elimination tournament. In other words, if you lose, you don't advance. You see the same thing in the NCAA March Madness tournament and NFL playoffs.
What's interesting about single-elimination is that the outcome is based on a sample size of 1 game. Sample size is a term we use to talk about how much data we're studying. Often (but certainly not always), a larger sample size provides results that are more statistically significant. For example, in this case, if the US had played Germany best out of 3 (or 5 or 7...) we would have expected Germany to come out on top, given their #1 ranking.
Of course, this assumes we're making valid predictions, and there aren't any omitted variables (like artificial turf) - two other topics we cover in our book.
But, as they say in the NFL, on any given Sunday, anything can happen.
Remember that when you're watching the US team take on England or Japan in the one and only final game this Sunday.