Friday, August 28, 2009

CONCACAF World Cup Qualification - take 2

If you haven't read the original article on CONCACAF World Cup qualification, I would recommend reading that first as this is a follow-up.

A common issue when using results to create rankings or make predictions is which results to include. Obviously I should include all results from the current qualification campaign. Including all rounds there have been 97 matches involving 35 teams. It's less clear what to do with qualifying matches for the 2006 World Cup, qualifying and the finals for the 2007 and 2009 Gold Cup and friendlies. I will be exploring this more scientifically in the future. For now I'll present the qualification probabilities for three versions - just using qualification results, including all 2007 and 2009 Gold Cup results, and including them but giving them only 50% weight.

The main difference between the predictions using just the qualification and either version including Gold Cup results is Mexico. Compared to the Gold Cups, or previous World Cup qualification campaigns for that matter, Mexico have performed quite poorly thus far in World Cup qualifying. In the two Gold Cups they reached the final, including a 0-5 thrashing of the United States at Giants Stadium. In qualifying, however, they have been mediocre and sit with 3 wins, all at home, and 3 losses, all on the road. The other five teams have had pretty similar results when you compare the Gold Cup and World Cup qualifying. So including the Gold Cup causes Mexico to look a lot better and hence be more likely to qualify.

Here are two tables. The first gives the percentage chance of each team finishing in the top 3 of the hex if you take just the qualification matches, include those of the Gold Cup but with only 50% weight and the last column gives the percentages including them in full. The second table gives the percentages for each team of qualifying overall if you assume that the CONCACAF team in the playoff has a 50/50 shot at advancing against the 5th team from CONMEBOL. I think that's a bit generous as the South American team should be a small favorite over most any of these teams, but it's a decent estimate for the top four teams; El Salvador and T&T would both be significant underdogs should they happen to make the playoff.

As you can see, Mexico is assigned a significantly better chance overall if you include the Gold Cup results into the model. Doing so doesn't affect Costa Rica much, probably because they are three points clear of Mexico. It effectively eliminates El Salvador and Trinidad and Tobago since the most plausible scenario that puts them through is edging out the Mexicans for fourth place in the group. For the US and Honduras, it reduces their chances of a top-3 finish by around 10% and a little under 5% for qualification overall. I think that Honduras is less impacted by the change because they are more likely to finish ahead of the US given that they are even on points and the US plays in Honduras October 10th. Also, because home field-advantage has been so important in qualification, it was not as big in Gold Cup qualifying, or for the US in the finals. Thus, including those results puts less importance on playing at home when predicting what will happen in the last four games. Even though Mexico looks stronger on paper when you include the Gold Cup results, the smaller benefit for the home team makes Honduras's match in Azteca look less daunting.

I don't have a perfect answer for what should be included. It boils down to how indicative you think results are from the Gold Cup of how well a national side will play in future World Cup qualifying matches. The problem is that most teams did not bring their best teams to the Gold Cup, especially in the 2009 version. For example, if you compare the lineups from the 2009 Gold Cup final, played July 26th, and the qualifying match, played August 8th, the US had only one player start both and Mexico six. The US opted to send their best team to the Confederations Cup and a B team to the Gold Cup. Brian Ching (IMUA!), who did not make the Confederations Cup squad due to injury, was the only national-team regular to play in the Gold Cup. The Mexican squad was more mixed, but it was far from their best and they clearly had objectives that went beyond winning the Gold Cup.

The Gold Cup happens every other year and seems to cycle so that the year after the World Cup it is more highly contested. This is likely because the winner there gets sent to the Confederations Cup, which is not true for the edition the year before the World Cup. The 2007 version was no exception and the national sides in it were more competitive. Thus, results from that version should be pretty indicative of qualification results. On the other hand, it took place two years ago, with some qualification matches taking place in 2006. I am not including the results from qualifying for Germany ’06 because I think that teams have changed enough in four years that those results don't say much about today, and it's going to be pretty similar looking back two or three years. I do think it is more reasonable to include the 2007 Gold Cup because the World Cup often serves as a cutoff with coaching changes and players retiring from international football frequently happening shortly after the World Cup ends.

If I had to guess, I'd say that the predictions excluding all Gold Cup results are probably the closest. There is good reason to exclude the results from either Gold Cup and I think even giving each half weight is probably too much. If I were the gambling type, I'd probably use the percentages somewhere between the first and second columns of the above tables, going closer to the No GC numbers than those in the GC-half column. Looking at Mexico in particular, my subjective view is that they have not looked very good in qualifying and I think those results are more indicative of their ability to get results going forward than those from either Gold Cup. Having said that, one of the major points of this blog is to objectively look at results, which is why I have presented the probabilities for the other two versions.

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