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FiveThirtyEight

Politics

Nice goal, boys.

I’ve gotten a couple of e-mails asking why the Soccer Power Index regards the United States as only about even-money in its second-round match against Ghana even though it has the more favorable ranking by some margin — it was 16th in the world in the SPI rankings prior to today’s games, whereas Ghana was 32nd.

The main reason is simply that we assign a home continent advantage bonus to Ghana (and the other African clubs), assuming that playing in your home continent is half as valuable as playing in your home country. I know, the African nations haven’t played very well this year — but they also haven’t been disastrous given injuries, some tough draws, and the fact that none of them were really in top form heading into the tournament. In any event, there’s pretty strong evidence that home-continent advantage exists, both from our research, others’ research, and anecdotal evidence: look how Europe performed in 2008 as opposed to 2004, for instance. A relative handful of matches aren’t really enough to undo that. But if you did remove the home-continent advantage bonus, the United States would be 60-40 favorites. (Hypothetically, if the game were played on U.S. soil, we’d be 79 percent favorites to advance, and if it were played on Ghanian turf, just 37 percent; home field advantage is very important in international football.)

The other reason is that, while the United States has a considerably stronger attack/offense rating (2.32 rather than 1.44; the numbers roughly correspond to the number of goals that would be scored against the 75th strongest team in the world on neutral turf), Ghana’s defense rating is stronger (0.80 versus 1.03; lower numbers are better in this case). SPI’s win probability estimates are not completely linear and what we’ve found is that the defense rating tends to be somewhat more important in games played against teams in the top several tiers of international football, which describes most every team that will play in the knockout stages unless New Zealand somehow makes it.

And this is not a very defensively-minded U.S. club: we’re a fit, uptempo, attacking team, which makes for really exciting soccer — but also one that can concede a lot of good opportunities to opponents, whereas it’s typically been some of the stodgier, more conservative sides that overachieve in the knockout stages. I don’t think we should change a thing, by the way, as the differences are quite minor mathematically speaking, but this is something that could come into play at the margins.

SPI is a pretty blunt instrument, so if someone wanted to make the case that there’s a clear favorite here, I probably wouldn’t debate them. For instance, it only “knows” via indirect evidence that Michael Essien is injured for Ghana. It assumes that the same basic strengths and weaknesses that apply in the first 90 minutes carry forward to extra time, when in fact our strong fitness could give us an advantage there. And although it doesn’t assume that penalty kicks are random — there is actually a decent amount of skill there, from what we’ve found — it does so in a fairly indirect way, and won’t know for instance that Landon Donovan has a reputation as a very strong penalty-taker and Tim Howard a very strong penalty-saver.

Still, from the football I watched in this tournament, I had the impression that the U.S. and Ghana played about equally well: the U.S. got 5 points out of its group to Ghana’s 4, but their group was somewhat tougher. Both teams had one really poor half — the first half against Slovenia for us, the second half against Australia for Ghana, when they failed to score against 10 men — but otherwise played quite solidly, without exactly making it look easy.

Undoubtedly, however, these are benchmark games for the United States. It’s not easy to beat Ghana in a World Cup played in Africa, and it’s certainly not easy to beat a team playing as well as Uruguay should we get them in the quarterfinal. But these are the kinds of matches we’ll have to start winning, and with some consistency, if we’re going to progress into the next tier of international football.


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