As a young boy growing up in Portugal, Luís Amaral loved playing, watching and talking soccer. Amaral and his friends passionately debated about which players were "the best."

But, it was just a matter of opinion. Unlike baseball and basketball, there isn't a lot of statistical information detailing how each soccer player contributes to a match.

Though their analysis, Amaral and his team were able to objectively rank the performances of all the players in the 2008 European Cup tournament. Their results closely matched the general consensus of sports reporters who covered the matches as well as the team of experts, coaches and managers that subjectively chose players for the "best of" tournament teams.

"In soccer there are relatively few big things that can be counted," said Amaral, professor of chemical and biological engineering with the McCormick School of Engineering and Applied Science and senior author of the paper. "You can count how many goals someone scores, but if a player scores two goals in a match, that's amazing. You can really only divide two or three goals or two or three assists among, potentially, eleven players. Most of the players will have nothing to quantify their performance at the end of the match."

To find a quantitative way to rank players, co-author and Northwestern graduate student Josh Waitzman first wrote software to pull play-by-play statistical information from the 2008 Euro Cup website.

This type of extensive statistical information is usually only gathered for important matches, Amaral said. Amaral and Jordi Duch, the paper's first author and an assistant professor of applied math and computer science at Universitat Rovira I Virgili in Spain, used the data to quantify the performance of players by generalizing methods from social network analysis.

"Researchers have developed new computational techniques to measure and rank the success of soccer players based on an objective measure of performance instead of opinion. (Credit: iStockphoto)"

Source: Northwestern University