Some Light Statistical Reading: Why I Use Relative Measures Instead of Absolute Measures

One of the cool experiences I have had since my post showing the undeniable correlation between squad transfer cost and table position went live last Thursday was being contacted by none other than Stefan Szymanski, one of the co-authors of Soccernomics.  Stefan was quite complementary in his email to me, with much of the content in the email falling along the lines of his column in the Evening Standard.  He also attached four of his academic papers he's written over the last two decades, which was a treasure trove of data and analysis that was behind many of the chapters of Soccernomics.  I have linked to each of them at the end of this post, but being academic papers each of them has a fee associated with them.

Of the four, the most enlightening to an American sports fan would be the paper he co-authored with Stephen Hall and Andrew Zimbalist in the Journal of Sports Economics entitled "Testing Causality Between Team Performance and Payroll: The Cases of Major League Baseball and English Soccer."  This paper does a great job comparing the ability to "buy trophies" in US baseball and English soccer, with far more in-depth analysis than I ever could perform.  Their main goal was to determine causality - does pay build better teams, or do better teams beget high salaries?  What's great about this piece is that it clearly explains the authors' approach to which measurements they use in their analyses and why.  I am often challenged as to why I use multiples of an average and relative finish position, rather than absolute pay and points, and Szymanski, Hall, and Zimbalist summarize better than I ever could why these metrics are key.

"In particular, [in studying Major League Baseball] we focus on winning percentages in the regular season and payroll spending by each team relative to the average payroll spending of all teams for the season.  If wealthy teams can buy success, we conjecture, then the most precise measure of their spending is the ratio rather than the rank.  For example, given that luck still plays a part, then the team that spends the most is more likely to achieve the highest ranking if it spends 10 time the average rather than 5 times the average."

Essentially, outspending your rivals to greater degrees ensures a greater possibility of minimizing the effects of the noise generated by random events like injury, freak plays, etc.  The added benefit is that using this approach helps linearize the payroll data, and compensates for the natural diminishing returns as payrolls escalate to place in the top few league table positions.  The authors then continue later in the piece to explain why they look at long-term averages rather than point data from each season.

"However, given that there are numerous factors that may influence a team's performance in a particular season, many of them purely random, a more reliable test of the effect of spending might be to consider those teams that overspend during the long term to see if they outperform the rest."

This is exactly what the authors do in this article and what Szymanski and Kuper do in Soccernomics, with both approaches yielding regression equations that explain much of the variation between performance and team payroll.  It was with this approach in mind that I studied the Transfer Price Index and utilized MSq£ for my unit of measure when studying the effect of squad transfer cost on table position.

While I have chosen to highlight this paper due to the applicability of the excerpts above, I would recommend the four papers below to anyone interested in soccer econometrics.

Key Stefan Szymanski Papers

Hall, Szymaski, and Zimbalist. "Testing Causality Between Team Performance and Payroll: The Cases of Major League Baseball and English Soccer."  Journal of Sports Economics. Vol 3 No 2.  May 2002.

Szymanski and Smith. "The English Football Industry: profit, performance and industrial structure." International Review of Applied Economics. Vol 11 No 1. 1997.

Szymanski. "A Market Test for Discrimination in the English Professional Soccer Leagues." Journal of Political Economy. Vol 108 No 3. 2000.

Garcia-del-Barrio and Szymanski. "Goal! Profit Maximization Versus Win Maximization in Soccer." Review of Industrial Organization. Vol 34 No 1. February 2009.

A Thank You Letter to Paul Tomkins

The aforementioned side project that I had been working on is now up on The Tomkins Times. The post uses Paul Tomkins' Transfer Price Index database to make a pretty compelling case that contrary to Soccernomics' assertion, finish position is correlated to transfer fee expenditures. This clearly has big implications related to fairness within the league, ability to spend in the future due to heavy debt loads at some clubs, and will certainly be impacted by the forthcoming Fair Play rules. I encourage my readers to check it out. I'll have a brief post on Arsenal's performance against the new transfer metric that we developed at a later date.

Most of all, I can't sing Paul's praises enough. He reached out to me over half a year ago about running some analyses on his database. Unfortunately, I was not able to indulge him at the time due to the hectic summer I had with the wedding, business travel, and just getting my blog off the ground. Luckily, I saw a mention of Pay as You Play before I went on my honeymoon last month and it rekindled my creative juices. I contacted Paul, and was lucky enough that he was still interested. The rest is history.

Paul took a chance on a newbie that had a hot statistics hand, and I can't thank him enough. The data he has assembled is a statistician's dream, and I am so privileged to have access to it. More bloggers and writers need to be like Paul - engaging, understanding, patient, and above all non-judgmental and not egotistical. Paul is a true collaborator, seeking talent and engaging it when he sees it. And when it's especially "rough talent" like me (I know I am way out of my league when it comes to Liverpool knowledge), he's willing to continually work with the writer.

It's been an awesome experience over the last week, and I hope to repeat it in the future. If you're a fan of good discussion and analysis (especially related to Liverpool), pay the six dollars a month to be a subscriber to Paul's blog. I've been singing the man's praises, but the blog content is even better! Reward great talent, effort, and product when you see it.

PS - Special shout out to Paul's co-author on Pay as You Play, Graeme Riley. His reviews of drafts and continual suggestions throughout the development of the piece were invaluable. Trying to make a complex 12-page study reasonably readable for a wide spectrum of readers is no easy task, and Graeme played a large part in getting it there.

Thoughts and Predictions on the Semifinals

What started with 32 teams nearly four weeks ago has now come down to four teams and four matches over the next six days. I'd like to provide some commentary on the remaining teams, their performance to date, and some predictions for the semifinal round.

Demographics

While I am not using the Soccernomics model to predict outcomes in any of these final knockout rounds, I do find the demographics of each team to be fascinating. Here are the three constituents to the Soccernomics model for each of the four remaining teams (in descending order for each attribute).

Population

1. Germany: 81,757,600
2. Spain: 46,030,109
3. The Netherlands: 16,616,850
4. Uruguay: 3,361,000

In this category we see the Western European nations dominating with their size and population density. It turns out that Uruguay was the second smallest nation to participate in this year's tournament - only tiny Slovenia has fewer people to draw upon for their national team.

GDP per Capita

1. The Netherlands: $48,223
2. Germany: $40,875
3. Spain: $31,946
4. Uruguay: $9,426

Again, the Western Europeans dominate. The Uruguayans come in dead last in both population and GDP per capita, meaning the talent pool they pull from and resources they can dedicate to such a talent pool will be smaller than the other three nations.

International Experience

1. Germany: 709 matches
2. Uruguay: 688 matches
3. The Netherlands: 587 matches
4. Spain: 461 matches

Here's where Uruguay shines. Only four teams - England, Argentina, Brazil, and Germany - have played more international games than Uruguay. Ironically, all five teams are part of the elite group of seven to have won a World Cup (Italy and France being the other two), and four out of those five made it at least to the quarterfinals in this year's tournament (sorry, English fans). Argentina, Brazil, and Uruguay have combined to win half of the World Cups contested to date. Of Uruguay's total international experience, they have played 181 matches against Argentina and 66 against Brazil (only their experience against Paraguay comes close with 63 matches). These matches mean that 36% of Uruguay's international experience comes against perennial World Cup championship contenders. While some may be surprised that CONMEBOL's representative in this year's final rounds is not Brazil or Argentina, they shouldn't be so surprised. Given the right manager and team, Paraguay should do as well as they have due to consistently challenge themselves to play against nations that are much larger than them and who continually challenge for soccer's top prize.

Not that I am counting, but some may be interested in how this adds up for a Soccernomics line. Here you go:

• Netherlands (+0.3) over Uruguay
• Germany (+0.4) over Spain

Regular readers will recall from my previous posts that such small spreads in predicted goal differential mean the model can't accurately predict the outcome of the match. Instead, let's take actual tournament data to understand how each team has performed so far and is trending as the knockout rounds go on.

Play-to-date

As in previous posts, I turn to the Footballer-Rating system for objectively evaluating team's performances in matches. It appears that their website is about a match behind as they have only posted results through the round of 16 (curious US fans should note that the differential between the US and Ghana ratings were 0.4 in favor of the Ghanaians, although both teams recorded negative ratings). Figures 1 and 2 below show the semifinalists' ratings and rating differential by match, with the dashed lines representing the three match running average trendline for each team.

Figure 1: Semifinalist Footballer-Rating score by match with 3 match running average dashed trendline

Figure 2: Semifinalist Footballer-Rating score differential by match with 3 match running dashed average trendline

The figures provide a useful comparison to the results realized so far in the tournament by each team.

Spain is killing the opposition in rating differential and absolute ratings, but this has translated to three narrow onw goal wins and two losses. This is likely due to the fact that Spain has passed the most, had the highest touch differential, been the most accurate passer in these finals, and the Footballer-Rating system rewards passing as well as scoring goals. It's an aberration in an otherwise mediocre performance so far for the second best team in the world according to the FIFA rankings.

Uruguay, on the other hand, has performed erratically and thus has shown relatively small ratings differential versus the competition. It shows in the basic statistics as well - Uruguay ranks at or near the bottom versus the other three semifinalists in every major category. The Footballer-Ratings scores indicate the up-and-down nature of the tournament so far for Uruguay and its fans. It seems that the Uruguayans have been able to make goals (or stop them in the case of the quarterfinal match against Ghana) when they really counted.

Save for their final group play match against Cameroon, the Dutch have completely outclassed their opponents by winning their matches with a Footballer-Rating differential of 0.7 or greater. Their absolute ratings are a bit lower, suffering from tough second and third matches in the Group Play stage. They began to turn things around with a dominant Round of 16 match, nearly equalling their opening match drubbing of Denmark. The Dutch are the only team left to have won all of their matches so far, consistently rank in the middle two spots of the four teams left when it comes to key statistics, but have the highest goals-against average of the four remaining teams.

The German ratings are a bit odd given their performance to date. Something odd happened in the Round of 16 match against England, as Germany dominated the match yet received a -0.9 rating differential. Conversely, their 4-0 opening match win against Australia earned them a +1.5 rating differential. Regardless of the ratings, the German attack has been relentless and has yielded 13 goals with three 4-goal dominating performances. The Germans rank at the top of the shooting categories, and in the middle of the passing ones.

Predictions

Last round I only went 1 for 4 as I picked too many favorites and the wrong upset. I will try not to make that mistake this time.

Figure 3 shows the Footballer rating moving average for the last three matches as scored by the Amaral Lab.

Figure 3: Three match moving average of Footballer-Rating scores

The Spain/Germany semifinal will be interesting to watch. Both squads have been impacted by similar passing/attacking styles originating in The Netherlands - it should make for an exciting match. Outstanding, experienced play is what it will take to beat the young and fast Germans. I think it is too much to ask of the Spaniards to flip the switch at this point in the tournament and go from mediocre play to outstanding play. I see Germany's offense overwhelming Spain for an upset according to Footballer-Rating.

In The Netherlands/Uruguay match I am going to take the favorite. I think the Dutch are playing too well, too consistently to not make it through to the final. Along with the Germans, they seem to have been the best TEAMS of the tournament - each player knowing their role and supporting the team accordingly. While I know my Dutch friends approach each match with apprehension waiting for the classic Dutch breakdown, this team has seemed very focused on the matter at hand and resilient when presented with a challenge (i.e. being down 1-0 to Brazil). I think they're simply too good, and they will eliminate an Uruguayan team that has fed off luck and bucking the statistics in this tournament.

If my predictions turn out correct, it'll make for a repeat of the 1974 World Cup final match. If that is the case, it would be an exciting match to watch. It would be a shame to have to see such a gifted German team lose, but I think much of the world would be pulling for the scrappy Dutch to finally deliver the world championship they have come close to winning several times before.

Short- and Long-Term Statistics: World Cup Quarterfinal Predictions

Soccer Dad at Soccer Quantified provides a nice cautionary tale about the over reliance on statistics in trying to predict the outcome of individual matches like those in the World Cup. He provides a nice link to my "Statistics Are Just Numbers" post, and after reading his post I feel compelled to comment on the subtle difference in some of the statistics I have used during this World Cup.

There are two types of statistics that I have used to predict performance in this tournament - longer term demographic data within the Soccernomics model and shorter term team performance data within the Footballer-Rating.com model. They both serve good purposes at
different stages of the tournament. Let me explain.

Socceromics Model In Group Play

The Soccernomics regression uses demographic data and match results over decades to predict the most likely outcome of a match between two teams. That is to say that it will tend to make better predictions in larger sample sizes where individual matches have less
impact (i.e. not win-or-go-home). Team adrenalin and short term boost have less of an impact in group play matches than knock out round matches, both in the many games that must be played and in the fact that each team knows that they must perform over those many games. This makes the Soccernomics model better suited for group play, although many statisticians might argue that three group play matches per team and 48 total matches might still be a smaller-than-ideal sample size for such a model. I will let my last post be the judge of that.

There is an additional benefit of using the Soccernomics model in the group play rounds. It will not only provide a reasonable prediction over time, but it also plugs a gaping hole - no player rating data exists for such matches. As much as we'd like to have a more direct method to compare the teams in their group play matches, there is very little short term data available to make such comparisons. The high pressure qualifying matches that might be the closest environment to that faced by World Cup teams are completed six months prior to the start of the final tournament. Team composition, chemistry, and momentum have changed greatly in those six months. The friendlies that most teams play as warm ups to the tournament are just that - they are good warm up matches, but they are not anywhere as competitive as a World Cup match. Thus, we must turn to longer term demographic data at the outset of the tournament to get a reasonable idea of which teams are going to make it out of group play and which teams aren't.

Footballer-Rating Model in Knockout Rounds

The knockout rounds are a different matter. After three matches of group play action, we can quantify how well a team did against World Cup caliber teams in a World Cup setting. We can begin to understand which teams are lucky to be in the knockout rounds based upon their play to date, and which ones got into them by dominating their competition. At this point, a player or team-based metric that evaluates actual performance should provide a better judge of future near term performance than a long-term demographics based model. Enter Footballer-Rating's player metric model, which got seven out of the eight Round of 16 matches correct compared to the Soccernomics model that got five out of the eight matches correct. Statistically, the chances that the Soccernomics model is more accurately predicting the outcome of the knockout matches versus simply flipping a coin is only 16%, while the Footballer-Rating method's chances are 76%. Why is that?

Recall from my last post where I showed that the ability of the Soccernomics model to accurately predict a "not lose" situation greatly increases once predicted goal differentials rise above 0.5. The problem is that most of the disparity in team performance based upon demographics is gone by the time the knockout rounds start. There were only two matches in the Round of 16 where Soccernomics predicted goal differentials larger than 0.5, and in both cases the predicted winner actually lost the match. In one case the Footballer-Rating prediction greatly favored the opposite team, and in the other case it predicted a virtual draw (which did occur during regulation and extra time). Combine these low goal differentials with the fact that the knockout rounds cannot produce a tie, and we see that the Soccernomics model is not a good fit for knockout round predictions. The Footballer-Rating model, which looks at recent play at the same tournament, naturally provides better predictions.

Quarterfinal Predictions

Based upon the accuracy of the two models in the two different phases of the tournament, I will be using the Footballer-Ratings model for the rest of the tournament. However, it must be said that their is one shortcoming with that model - the authors of the website that compiles the team ratings are not updating it with knockout round match data. I would have liked to have seen such updates, as team performance can change throughout the knockout rounds as the quality of opponents continues to rise. Nonetheless, Figure 1 shows the Footballer-Rating team average scores from the group play stage.

Figure 1: Footballer-Rating average team scores from group play matches

From a previous post we know that a gap of 0.7 or greater means that the favored team's chance of winning that match is 75%. With each match exceeding this threshold, we're likely looking at a semifinals round with Brazil, Ghana, Argentina, and Paraguay. Given that Ghana's predicted gap is the smallest and Uruguay's stiff defense, I would expect that the most likely upset might come from that match. I think Germany has a reasonable shot at slowing down Argentina. The Argentines are flying so high right now that they simply must regress to the mean at some point, and teams that perform so well and all of the sudden hit their first serious challenge often choke up a little bit. However, while I think the Argentina/Germany match may be close, I don't think the Germans have enough to beat Argentina.

So, here's my prediction for semifinalists: Brazil, Uruguay, Argentina, Spain. It's been a CONMEBOL dominated World Cup. Why stop now?

Evaluating Group Play Against the Soccernomics Model

I've spent a number of posts talking about the Soccernomics predictions for World Cup group play outcomes. Now that group play is complete, it's time to evaluate how the model did at predicting outcomes and which teams greatly over- and underachieved versus their Soccernomics predictions.

Ability of the Model to Predict Group Play Match Outcome

One way to judge the accuracy of the model is to look at its overall count of correct and incorrect predictions of outcomes. I have added a third category, "D" for draw, to capture when a push might occur in a situation where a wager is made on a specific match. Figure 1 captures this count.

Figure 1: Count of matches where Soccernomics predicted outcome of win/loss was correct (1), incorrect (-1), and when a draw occurred.

As one can see, the Soccernomics model correctly predicted the winner of 24 group play matches, or 50% of the matches played. The next likely outcome was a draw, with the least likely outcome being an incorrect prediction. This suggests that if wagers were involved in the matches, one could stand to make a good bit of money in wagers without spreads that also utilized pushes.

Of greater interest, however, is under what predictions the Soccernomics model is most accurate. How big does the predicted goal differential need to be to ensure a higher likelihood of predicting the correct outcome of the match? Figure 2 answers this question by using a cumulative distribution function (CDF). A CDF is used to show the likelihood (y-axis) of finding a value equal to or less than the one of interest (x-axis). In this case, I have plotted (1-CDF) to more clearly show the separation of the accuracy of predicted outcomes based upon predicted goal differential.

Figure 2: (1-CDF) for the Soccernomics model's ability to correctly and incorrectly predict a match outcome, as well as a draw.

Two observations can be made about the Soccernomics model's ability to predict outcomes in World Cup group play:

• By a goal differential of 0.5, the model's ability to predict a "not loss" outcome is about 2:1. This gap grows as the goal differential progresses to 1.0. Any predicted goal differential greater than 1.1 means that the superior team will either draw or win the match with virtual certainty.
• The closeness of the "correct" and "draw" lines indicates that the model's accuracy is not good enough to differentiate between a win or a tie. This makes the push all the more critical in a situation involving wagers.

The importance of a win in group play is even higher than expected given the roughly equally likelihood of drawing or winning with such high goal differentials. As SoccerQuantified.com points out, the number of draws in this year's group play was completely normal compared to previous competitions (although an abnormally high percentage came in the first matches).

Performance vs. the Model

Given the model's predictions, I have also quantified which teams have over- and underperformed the most versus the model. One measure of this is the average residual from the model - see Figure 3 for a plot of these average residuals in descending order.

Figure 3: Average residual from Soccernomics model by nation

One can see that four out of the top five teams made the knockout rounds (Slovenia being the exception), and eleven of the fifteen teams with positive average residuals made the round of sixteen. This left only five spots for the remaining teams, meaning teams with a positive goal differential residual to the Soccernomics model were twice as likely to make the knockout rounds than those who did not.

Another way to understand which nations performed most consistently against their Soccernomics prediction is to look at the standard deviation of their residuals to the Soccernomics model. Figure 4 summarizes this data.

Figure 4: Standard deviation of residuals from Soccernomics model by nation

Nations with the smallest standard deviation of performance to the Soccernomics model present a mixed bag of overall performance. New Zealand and Slovenia ranked high on both lists, indicating they consistently outperformed their Soccernomics predictions. Cameroon pretty much conformed to their Soccernomics prediction given their average -0.1 residual and low standard deviation. England and Italy, by ranking low in average goal differential and with a low standard deviation, consistently underperformed against their Soccernomics predictions. Also note that Portugal has the highest standard deviation, which indicates their top spot on the average residual list is likely due to the outlier of the seven goal barrage against North Korea. This means Slovenia's performance was likely the most consistent overperformance in the tournament.

If there is a Tom Thumb award to be handed out, it's a toss up between Slovenia and Uruguay. Slovenia deserves special consideration due to how small and new their country is. They have only two million people, with a much smaller population base of 20-30 year olds that could play in the World Cup. Uruguay deserves consideration for their high score on the average differential scale, and their win in the Round of 16. To win that match they had to overcome both the Soccernomics prediction and Footballer-Rating.com prediction that both favored Japan. They will face a challenge similar to what the US faced in the first round - a Soccernomics prediction that favors them but a Footballer prediction that favors Ghana. If they make it through that match into the semi-finals, they will truly be a Tom Thumb winner. Until then, Slovenia's high average residual and low standard deviation make them the winner.

Notes About the Round of 16

As I stated here, the Soccernomics model predicted smaller goal differentials for the Round of 16 - only one match had a projected goal differential higher than 0.6. In fact, the one game that did have a projected goal differential higher than 0.6 ended up being an incorrect prediction, although it did fall into the second most likely outcome for regulation time score (a 1-1 draw) based upon group play matches with a predicted goal differential of 1.0 or more. On the other hand, the Footballer-Rating.com method of looking at group play performance of the two teams to determine likely match outcome predicted the correct result in seven of the eight matches (Paraguay's win against Japan was the one outlier). This model seems to be a much better predictor of outcome in the early stages of the knock out round. It will be interesting to see if this trend holds. The statistics team at Footballer-Rating.com does not seem to be updating team performances based upon knockout round matches, which will force me to rely upon the group play data. I would have preferred to do a three match running average to capture the effects of playing against tougher opposition as the competition goes on.

Observations on the Round of 16

This time it will be much closer

It's been an exciting two weeks of group play, but now we know who is in the knock out rounds. We start things off early Saturday morning with the Uruguay/South Korea match and finish things up on Tuesday with a clash of the Iberian Peninsula.

In commenting on Round of 16, I will rely on two statistical methods for quantifying performance: the Soccernomics model for international matches that relies exclusively on demographic data, and the Footballer-Rating.com method that judges past performance in the tournament. The projected goal differential (Soccernomics) and average player rating by team (Footballer-Rating.com) are shown in the figure below.

Figure 1: Soccernomics and Footballer-Rating.com predictions for the Round of 16. Both scores are differences between the two teams expressed as (Left hand team - Right hand team)

As I mentioned in my last blog post, the United States/Ghana match is the only one where a team has at least a 1.0 goal differential advantage according to the Soccernomics model. Based upon matches with similar projected gaps, the US stands a good chance (11.5/16) to advance. Interestingly enough, the US/Ghana match also shows the biggest gap between the Soccernomics and Footballer predicted performances.

Per the original study that produced the Footballer statistical method, a differential of 0.75 or greater meant that the favored team had 3:1 odds of winning the match. This would mean that Ghana, Argentina, The Netherlands, and Spain are heavy favorites to win their first knockout round matches if they can maintain their group play form.

On the demographic front, there are some interesting points to be made.

• Only 6 of the 16 teams has a GDP per capita less than $10,000, and all but one of those 6 are from Central or South America. Ghana, the poorest country in this year's tournament, is the one sub-$10,000 country not on the American continents.
• At the opposite end, there are 6 teams with a GDP per capita greater than $30,000. This group consists of the four European teams left in the tournament, the US, and Japan.
• Every team in the knockout rounds has played 400 matches or more of international soccer competition. This meant most of the African teams were doomed from the outset, with Ghana being one of the few African teams with the requisite experience to get through group play.

Finally, some commentary on the Germany/England match. This might be the most even match of the Round of 16. Soccernomics says it is dead even, while Footballer-Rating.com has the Germans coring 0.3 points higher on their scale during group play. Perhaps we should just be listening to this octopus after all, because the statistics are clearly a wash on this match.

Happy World Cup watching over the next four days, and go Team USA!

That's Why They Play The Games, Part IV

Time for some revenge for 2006, boys!

They were the richest of nations, they were the poorest of nations...

A description of tomorrow's USA/Ghana knockout round match might as well begin with a twist on that classic beginning to A Tale of Two Cities. Demographically the two nations couldn't be more different. Not only does the US hold a sizable advantage in wealth, but it also holds a huge advantage in terms of population. Let's dive into the numbers to see what Soccernomics can tell us about this match.

Population

• Ghana: 23,837,000
  
• United States: 309,488,00
  

GDP per capita

• Ghana: $671
  
• United States: $46,381
  

International Experience

• Ghana: 389 matches
  
• United States: 403 matches
  

These advantages translate to a predicted 1.0 goal differential in favor of the United States. In fact, this will likely be the largest projected goal differential of any match if the first round of the knockout stages. In the Soccernomics model at World Cup 2010, a projected goal differential of 1.0 is huge. Only 15 matches in group play, or less than one third, have been projected to have a goal differential greater than or equal to 1.0. Fourteen of those matches have been played so far, with today's Switzerland/Honduras match being the fifteenth. In the 14 matches so far, the record of the teams favored by one goal or more has been:

• Wins: 9
• Draws: 4
• Loss: 1 (those plucky Slovenians over Algeria)

I don't have the statistics of how well the US and Ghana do at extra time or penalty kicks, but let's call it 50/50 so that the draws are split evenly. This means the US has at least an 11/15 chance of moving on if World Cup group play is any guide, and possibly as high as 12/15 if the Swiss meet their Soccernomics prediction and win today's match.

The one caveat to all of this is that Ghana is playing great soccer right now. As I noted in my last post, they have outplayed their opponents in group play to a greater degree than the US, but the gap is much smaller when you look at their absolute average team ratings (Ghana's 1.2 vs. US's 1.0). This should be a great match, and a great tuneup for whoever moves on to face the winner of the Uruguay/South Korea match.

There was a time late in the match on Wednesday when I thought I would never be posting a fourth installment of my series of posts. Anyone who tells you they felt differently, that somehow they hadn't given up hope in the closing minutes of that match, is either a liar or delusional about soccer. Landon Donovan's goal not only saved the US's run in the Cup, but validated what many of us believed to be true - this team is a world beater that deserves to be in the knockout rounds. Informed pundits and players around the world know this is a special team for the US, and they have got a good draw in the knockout rounds. They have accomplished goal #1, and can now pay lose and without fear. If they can beat Ghana, they have a good shot at running through to the semifinals. And if this team gets up a head of steam, they can be VERY dangerous. Just ask Spain and Brazil. I'm not saying they can win the Cup, but I am saying they can make a deep run and make the knock out rounds very interesting.

US Men's National Team, you've already made you nation proud and provided us with some of the most dramatic games of the cup. Thank you so much. Now it's all about continuing to shock the world. Let's go boys!

That's Why They Play The Games, Part III

The weight of soccer in the US is on their shoulders

Maybe I am being a bit overly dramatic. Soccer has flourished in this nation over the last 20 years without consistent success at the World Cup, and one set back here can't possibly stop that growing tide of support. It certainly can slow it, and a win would help accelerate it.

On the other hand, tomorrow's match against Algeria is that important. Win, and the team erases eight years of heartache - a time without a win at the World Cup. Win, and the team moves on to the knockout rounds, possibly as the top seed from its group. Win, and the team caps what would be considered a great 2010 World Cup group play campaign. Lose, and it is all over. Draw, and it's possible we back our way into the knock out rounds and go 12 years without a win at the World Cup. It's simple - win or fail to meet the public's expectations.

Building upon my two previous posts on the US team at this World Cup, let's see how the two nations stack up based upon the Soccernomics model.

Population

• Algeria: 34,895,000
• United States: 309,488,000

GDP per capita

• Algeria: $4,027
• United States: $46,381

International Experience

• Algeria: 250 matches
• United States: 403 matches

The United States' nearly 10-to-1 advantage in population, 11-to-1 advantage in GDP per capita, and nearly 60% advantage in experience yields a 1.0 goal differential advatage. They'll need to maintain such an advantage to move on to the next round of play.

My personal prediction

I suspect that the Algerians will pour as much of their team into the US end of the field as they can for the first 15 minutes of the match. The US team concedes nearly 1/3 of the World Cup goals scored against it in the first 10 minutes of a match, and they have been true to form in the first two group play matches. The US team also has never won a World Cup match when their opponent scores first. These two facts combined have led to three wins in the last six World Cups. Alegeria will come hard and fierce, and the US defense will have to do what they haven't done so far in this World Cup - not allow a score before the 15 minute mark. If they do this, the US stands a good chance to win the match. If they don't, the best they can hope for is a draw.

I think the US team will surprise a lot of people in this match. Reading the few post-match interviews available after the Slovenia draw, I got the sense that the first half of that match was a wake up call to the team. Several reports indicated that the team took it upon themselves in the lockerroom to play to their full capabilities, the result of which was the flurry of the second half that should have seen the US win that match 3-2. That is in the past, but it provides a very effective motivator. These guys know what they represent, and it's more than just US players good enough to earn European league pay days.

They represent a turning point in our nation's love/hate relationship with soccer. There's something intangible out there in the US fan's psyche right now. We're tired of thuggish, spoiled, 'roided up players in our other professional sports, and we're longing for players who play for a love of the game, for national pride, and for a beauty that has been corrupted for too long by leagues and players bent on extracting a better contract or a better stadium deal. Our nation's love for the Cup and the sport, no matter what idiots like Glenn Beck and G. Gordon Liddy say, is measurable and it is growing. This game is much bigger for US supporters than making a knock out round. It's about legitimizing the love we have for our team, what they represent as sports professionals, proving the usual American soccer naysayers wrong, and showing what this game represents for those of us largely fed up with professional sports in America. I will be watching the match live, 7 AM Seattle time, and holding my breath for 90 minutes hoping for an American win.

My prediction is US 2-1, without conceding the first goal. Good luck, boys! And even though they may not be English, DON'T SHOOT UNTIL YOU SEE THE WHITES OF THEIR EYES!

World Cup Performance vs. Soccernomics Predictions Through Two Games

Continuing with my analysis I started after the first matches were complete, the table above reflects the average of the teams' residuals from the first two matches of group play versus the Soccernomics model. My spreadsheet used to calculate these values can be found here.

Germany's 0-1 loss to Serbia dropped it from the top position it held after its first match, and Portugal has now replaced Germany at the top of the list with their 7-0 clinic they put on against North Korea. I will single Slovenia out for unique praise later in this post. Uruguay, Paraguay, and Argentina all moved up with their performances in the second match, while the Netherlands and Ghana have maintained their positions from the first match. England, USA, and France all dropped substantially from last week as their either drew or lost in matches where they were heavily favored.

Slovenia's consistent performance versus the Soccernomics model deserves much praise. One way to measure this consistency is to look at the standard deviation of each team's performance. It's a bit straightforward right now given only two matches have been played, but will become more useful as we close out group play with the third match. The table below shows each teams' standard deviation of residuals to the Soccernomics model.


We can see teams like South Africa, South Korea, Germany, Portugal, and North Korea which experienced inconsistent results from the first to the second match exhibit the highest standard deviation in their goal differential residual. At the top of the list is Slovenia - showing virtually zero deviation in the first two matches. Slovenia is not only outperforming the Soccernomics model, but they are doing so in the most consistent manner.

Finally, we are beginning to get an idea of what the knockout round seeding will look like. The table below shows the current matchups as they stand after the second round of group play (click on the bracket to see a full view of the path to the World Cup championship match).


Only two spots (The Netherlands and Brazil) have been clinched before the third round of group play. Another three (Portugal, Argentina, and Chile) are virtual locks. That leaves 11 spots up for grabs in the final round of group play. We start with Mexico, Uruguay, Korea, and Greece battling for spots by looking for a win on Tuesday. The big Group C games come on Wednesday, which will determine which two nations - England, Slovenia, or the USA - move on. By Friday, we will be treated to Portugal vs. Brazil, Chile vs. Spain, and Switzerland vs. Honduras - all of which will impact the knockout round seeding. I suspect that the final seeding will look very different than my table above.

Enjoy this final, hard four days of group play!

My reaction to the USA/Slovenia match

I see everyone grabbing everyone else. Where's the foul?

At the risk of deviating from my usual statistical discussions, I feel compelled to comment on the most exciting and controversial game in the World Cup so far. So much about the match goes to the heart of the game itself, which is my ultimate concern. Numbers are nice, but they're meaningless if the game isn't beautiful.

Other than a few tweets, I've generally restrained from commenting on the Slovenia/USA match. I am not interested in sounding like a sore loser, and while there certainly appeared to be plenty of bad officiating it is always best to wait a day or so to see what kind of opposing points of view might emerge. In doing so, one gets a complete picture and makes a more informed commentary. In this case, I must mention how grateful I am for Erik Renko's feedback.

Erik started following my twitter feed a while ago in the run up to the World Cup. Erik being Slovenian, he and I were bound to have some interesting discussions about this inevitable group play clash. As my previous posts indicate, I have a healthy bit of respect for the Slovenian national team for outperforming the Soccernomics model. The discussions with Erik, and the insight he has provided me both pre- and post-match into the Slovenian supporter psyche, have been a wonderful experience made possible by our Web 2.0 world. If you want great soccer insight, I suggest following Erik.

To begin my reaction, I must refer to this NY Times blog entry that Erik sent me this morning. In it, the author provides some pictures and video that show some of the grabbing and pulling by the US team that may have led to the referee's call to disallow the goal. The author of the blog post argues half tongue-in-cheek that there might be some offenses worthy of such a call, while also acknowledging that similar actions were being taken by Slovenian players.

I think any objective fan can look at the two photos and agree that there was a lot going on during that free kick that isn’t allowed. So maybe some of us didn’t like what Coulibaly saw, or that he chose to pluck out a foul by a United States player instead of one against a United States player. But you can’t say nothing happened.

While there certainly are such offenses on both sides, I fall on the side of the referee not taking action for the exact reason that everyone was holding and grabbing. The Slovenian player holding Michael Bradley was probably the worst offender from either team, and Maurice Edu's footwork for the goal really didn't seem to benefit from any US player's hold. In fact, it was quite the contrary as he too was impeded (even though the official FIFA ruling said the foul was by Edu). On balance, it looks like the usual pushing and shoving on a set piece that should have resulted in a no call.

These pictures and the insight they provide also bring up the sensitive topic of instant replay. Many in the United States are used to instant replay due to its use in American football and to a lesser degree in basketball, hockey, and baseball. Many would like to see it applied to soccer for situations like those in the USA/Slovenia match. There are a lot of logistics for instant replay - would it be reviewable only by FIFA officials in a booth upstairs, or would managers have the ability to throw a flag to challenge a call a la the NFL? To me, any implementation would be a travesty of the first order because it wouldn't really resolve the subjectivity of fouls in soccer. Applied directly to this case, what would be the grounds for reversing the prior call? As already discussed, other than Landon Donovan who was taking the free kick, everyone was violating the rules of soccer in some way or fashion on that set piece. It's likely the call would have stood, and would we really want to stop the game for five minutes for an equally arbitrary reversal based upon one of the likely ten infractions committed on the play? This is where the American fan needs to think like a global fan, respect the game as it is on this topic, and move on.

The emphasis shouldn't be on instant replay, but instead on better officiating. I don't hold any conspiracy theories about this referee, but I have read enough to know this isn't Koman Coulibaly's first run in with controversy. The call against the US goal also wasn't the first questionable call in the sequence, and much of the match was marred by inconsistent officiating that often didn't make the calls that should have been made. No cards or fouls were given to Clint Dempsey's body slam of a Slovenian defender, nor Slovenian defenders' several tackles at the edges of the penalty box. The card given to Robbie Findley for a handball in the first half was ludicrous. In general, the first half was light on cards while the second half saw Coulibaly dealing them out as if they were going out of style. It's clear to me that Koman Coulibaly isn't experienced enough nor has good enough discernment to be a World Cup official. He reminds me more of the quality of referee we have to deal with in MLS.

Finally, Erik was able to relate how the second half of the Slovenia/USA match was deja vu for Slovenian fans. In Euro 2000, Slovenia went out to a 3-0 lead before conceding a draw after Yugoslavia came back with three goals later in the match. Erik used this as an example of a "lack of finishing instinct" in the relatively new Slovenian national team. As he said,

[Number] of [international] matches, short history and relative lack of winning habit prevented [Slovenia] from winning [the] match vs. USA.

As I said in my response,

Oh that darn third term in the Soccernomics equation!

It's clear to me that if the Slovenian team continues to outperform expectations, it will get the necessary experience it needs to close the gap it has to the other European national teams in its backyard. Regardless of the bad officiating, I have acquired a healthy respect for the Slovenian national team. We Americans like underdogs, and we love to embrace nations like Slovenia who have successfully transformed their nation since the fall of authoritarianism. Sadly, this match may mar many US fans' outlook to a team we all should be rooting for if they make it to the knockout round.

That's Why They Play The Games, Part II

This is what a potential giant killer looks like

This Friday the US Men's National Team resumes its quest to qualify for the knockout round in the 2010 World Cup. Winning this match would not only instantly erase the memory of the winless campaign in 2006, but it would also allow the US to control its own destiny within the group. A draw is not a disaster, but also not preferable. A loss, and Bob Bradley's boys are in deep trouble.

This is also a very different match psychologically than the England match. The US is the clear favorite going into this match. They cannot be happy with coming away with a draw - the pressure is on for a win. And the weight of an awful 2006 campaign all comes down to this one match. What a difference six days make - the high of the draw against England must be forgotten and winning this match must be all that matters. How will this impact the play of the US team, which is not accustomed to be under such pressure?

So how would Soccernomics evaluate this match?

Population

• Slovenia: 2,059,470
• United States: 309,488,00
  

GDP per capita

• Slovenia: $24,417
  
• United States: $46,381
  

International experience

• Slovenia: 73 matches
  
• United States: 403 matches
  

All of this adds up to a 2.0 goal differential in favor of the United States. In this case, I would argue that the Soccernomics model is way over-predicting the likely outcome. Slovenia is a scrappy team always happy to play the upset role in a tournament. Nothing would make them happier than to take down the US, breaking up the US/England duo that nearly every commentator has seen coming out of Group C since the tournament seeding was announced. If the US doesn't play smart soccer, better defense than the first fifteen minutes of the England match, and make great attacks they may find themselves effectively eliminated from the tournament by the end of the day if they lose and England defeats Algeria.

My personal prediction, as a hopeful fan of the sport in America, is that the US team wins the match 2-1 and begins to convince the world and our nation they are for real. Either way, it should be a great match.

On the other hand, you could be like my tweep Boco_T, blindly follow the Soccernomics prediction, and end up getting the score dead on while most took the other team big.

First Game World Cup Performance vs. Soccernomics Predictions

Building upon my previous post, the table above shows the residuals for each team after their first match (except South Africa and Uruguay, who played their second match today) in the 2010 World Cup. A residual is the difference between an observation (goal differential in the first match) and the predicted value of the model (predicted goal differential of the first match according to the Soccernomics model). Residuals are useful in:

• Determining which observations are over- or under-performing versus the model
• Determining whether the model (regression equation) satisfies the statistical tests required of it

I will continue to use the residual approach to quantify how each team is doing against their corresponding Soccernomics predicted performance as both the second and third matches are completed for all teams. At the end of group play, I will be able to comment as to which teams were the biggest over- and underachievers in the tournament, as well as comment as to whether or not the Soccernomics model actually applied well to the tournament.

Before getting to that point, however, we can gain some useful observations from each team's first match. Germany's top position in the list, given a 4-0 drubbing of Australia, is not a surprise. As I have said in previous posts, Slovenia can easily play this tournament's "giant killer" role if they keep up their great start and tie or beat the US and England. Finally, even though the Dutch and Danes only had a 0.2 predicted goal differential, Holland's 2-0 win moved them to the third spot in the ranking.

At this point, as only one game has been played, the list is basically a reflection of who won and lost. The bottom three teams are the teams who lost to the top three - the bottom half is an inverse of the top half. As group play goes on, this list will get more jumbled and I will provide commentary as to the bottom three teams.

Finally, how about the Swiss upset of Spain today? Spain, favored by nearly a full goal in the Soccernomics model, finds itself in the bottom of the rankings around Algeria, Serbia, and South Africa. They will be playing catch up to Chile and Switzerland the rest of the way, hoping one of them stumbles in their next two matches. Perhaps there is hope for the rest of the world against the Spanish juggernaut that the press wants to prematurely crown champions.

World Cup & Soccernomics, Day-by-Day

In this earlier post I mentioned my friend's basic World Cup template that users can modify to suit their own purposes. I have done so, blending the GDP, population, and international soccer experience statistics from an earlier post to integrate the Soccernomics model results for each World Cup group play match. Using a bunch of VLOOKUP functions and pivot tables, I can get a good snap shot of summary statistics - both from what the model predicts and how each team does against the model. My work-in-progress spreadsheet can be found here.

I will use this spreadsheet throughout the tournament to comment on which teams are over- and underachieving against their predicted, historical average. The first attribute I'd like to highlight is which teams have the most and least difficult group play in the tournament based upon the Soccernomics model. Predicting the goal differential for each match and then using a pivot table to derive the average value for each team produces the table below.


As I mentioned in this post, Slovenia will be giant killers in this year's tournament if they can hold their own against the USA and England in their final two matches. What also jumps out at me on this table is the shear number of African nations at the top of the list - those facing the toughest climb. It speaks volumes that Ghana has been able to win, while all other African nations have either lost or drawn their matches.

In the next day or two I will post on how I will evaluate how each team performs versus their Soccernomics model prediction.

Outperforming the Soccernomics model: Slovenia and Ghana

Yes, the Slovenian goal was that big of a deal.

In a recent post I commented on how the Soccernomics model for predicting international competition goal differential applied to the England/USA match. In this post I will use that same model to show how big the wins by Ghana and Slovenia were in this weekend’s World Cup competition.

Ghana and Slovenia represent two ends of the Soccernomics model spectrum – some might say the wrong ends to be on if you want to succeed in international soccer. Slovenia is perhaps the newest team on the block, having played the fewest international matches of all the participants in this year’s competition. This is due to the fact that they only became a nation in 1991 as a consequence of the breakup of Yugoslavia (I have chosen to assign the Yugoslavian matches to its biggest successor – the nation of Serbia). Interestingly enough, Slovenia does possess a moderate amount of wealth and thus has a reasonable GDP when compared to other nations. Ghana, while having over fifty years of international soccer competition under its belt (nearly ten times the matches of Slovenia), is the most impoverished nation in this year’s World Cup. While Slovenia pays a far bigger price for its lack of experience in the Soccernomics model, both nations are often the underdog when using the model to predict match outcome. Let’s see how big of a disadvantage each team faced in their first matches.

Sources of Data

Before going much further, a comment must be made about the data sources used in this analysis.

• GDP: Throughout this post, I have used IMF data found in this Wikipedia article.
• Population: Throughout this post, I have used the data found within this Wikipedia article. As one can see, there is no real authoritative source for population data – the list is compiled from several reliable sources. The Slovenian government and UN estimates were used as sources for the populations of Ghana, Slovenia, Serbia, and Algeria.
• International Experience: This is perhaps the weakest data set in my study. I have used Russell Gerrard's AIFR data set, which was also used by the authors of Soccernomics. The main liability of this data is that it is only current through 2001, thus the last nine years of experience are not included in my analysis. This means that a few of the ratios, especially for a country like Slovenia where over half their experience is missing from its total international match count, are a bit off. This risk is somewhat mitigated through the use of natural logs in the model. As an example, doubling Slovenia’s experience and assuming Algeria played no matches between 2001 and 2010 reduces Algeria’s goal differential advantage by 1/3. That means that any observation we observe from the model is still likely real and significant. The risk continues to decline as more established teams (i.e. Ghana and Serbia) face each other. If anyone has any ideas where I might find data for international matches between 2001 and 2010, I am all ears.

Ghana vs. Serbia

This match represented the second chance for an African nation to claim a full three points at the first African World Cup. Before ever starting the match, the Ghanian team were underdogs, but just how big?

Population

• Ghana: 23,837,000
• Serbia: 9,850,000

GDP per capita

• Ghana: $671
• Serbia: $5,809

International experience

• Ghana: 389 matches
• Serbia: 578 matches

Serbia has nearly a nine-fold advantage in per capita GDP, a nearly fifty per cent advantage in international experience, and a nearly a two-and-a-half-fold disadvantage in population. This equates to 0.5 goal differential advantage for Serbia – certainly an advantage, but not a huge one. Thus, the victory by Ghana, representing a 1.5 goal residual from the Soccernomics prediction, may be more symbolic in its overperformance.

Slovenia vs. Algeria

Slovenia has played the role of world beaters over the last decade, making shocking runs in Euro 2000, qualifying for World Cup 2002, and defeating the Russians in the European playoff for qualification at World Cup 2010. Just how big of an underdog were they in the opening match?

Population

• Slovenia: 2,059,470
• Algeria: 34,895,000

GDP per capita

• Slovenia: $24,417
• Algeria: $4,027

International experience

• Slovenia: 73 matches
• Algeria: 250 matches

Slovenia’s population is clearly better off economically than their former Serbian brethren as well as their Algerian opponents. However, they suffer greatly in the Soccernomics model with less than one tenth the population and one third the international experience of Algeria. This translated to a 1.0 goal differential advantage for Algeria. Slovenia’s victory, which translates to a 2.5 goal residual for the team, is huge. If Slovenia can tie or win against the US (1.7 goal advantage) and England (2.3 goal advantage), it will have likely completed one of the best performances against the Soccernomics model of all the teams in this year’s World Cup.

That's Why They Play the Games

The ghosts of World Cup 1950 that will stalk England on Saturday

The Rematch is almost upon us, and it's only appropriate that I turn to the Soccernomics model for national team performance to provide a prediction of the possible outcome. If two teams, i and j, face each other the Soccernomics model uses the following equation to predict goal differential:

GD(ij) = 0.137 ln[pop(i)/pop(j))] + 0.145 ln[GDP(i/GDP(j))] + 0.739 ln[exp(i)/exp(j)] + 0.657 for home team

In the case of England and the US, no one is the home team so we can drop the final term in the equation. Now we turn to the population, GDP, and experience terms.

Population

• England: 51,456,400
• US: 309,449,000

GDP

• England: $35,334
• United States: $46,381

Experience:

• England: 780 matches
• United States: 403 matches

Plugging these variables into the above equation yields a 0.203 goal differential advantage for England. England greatly benefits from their nearly 2-to-1 advantage in international experience that counts nearly six times as much as the other variables. For all the smack talk from English fans, this is hardly an advantage in the World Cup.

This match will likely be far more even than some would think. It's certainly within the United State's capability to win it. Both teams are in top form, and everyone is hoping for an outstanding clash worth the 60 year wait.

I have only one thing left to say.

"DON'T FIRE UNTIL YOU SEE THE WHITES OF THEIR EYES, BOYS! BEAT ENGLAND!!!"