Major League Soccer has long been notoriously difficult to bet. The league’s byzantine rule book creates a level of parity unlike any other soccer league in the world, with extra headaches from long-distance travel and all kinds of weather.

But as MLS becomes more popular, and as sports betting becomes more widespread, more people are betting on the league like they do for Europe’s top competitions.

This has caught the eye of one of the world’s best-known authors on the finances of global soccer, University of Michigan economics professor Stefan Szymanski. His book “Soccernomics,” cowritten with Paris-based Financial Times columnist Simon Kuper, has been a must-read for fans for more than a decade.

Among Szymanski’s most famous theories is that, in European soccer, you can get a pretty good prediction of how the standings will finish by using players’ estimated valuations on the global database

Take each team’s aggregate value, create a home-field advantage factor based on historical results, run the formula, and you get a prediction model. Then comes the fun part: comparing the model’s predictions for a game to the betting odds.

In the current English Premier League season, for example, Szymanski’s predictions have a 51.7% success rate to the bookies’ 47.6%. Last season, his success rate was 52.9% to the bookies’ 51.3%, and his preseason-standings picks had 14 of the 20 teams within one place of their eventual finish.

Recently, Szymanski been working on whether his same model applies in MLS, using results from 2015 through 2020. He came quite close: a 52.3% success rate to the bookies’ 52.8%. The two data sets’ predictions differed on just 12 games out of 2,258.

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But what really struck Szymanski was another stat: Over the same six years, the home team won 52.2% of games, the away team won 23.9% of games, and 23.9% were draws. By contrast, in the Premier League — which has star-studded powerhouses at the top but also a healthy share of underdog upsets — the home team won just 45.7% of games, the away team won 30.3%, and 24% were draws.

It seems obvious that if the better team is playing at home, it should be more likely to win. What the data really show is that the talent gap between most MLS teams is small enough that playing at home matters significantly.

“I thought there’s enough variation [in Transfermarkt values] in MLS these days” that the values would matter more, he said. “It definitely was not what I expected.”

Szymanski’s data might even under-represent the importance of home field, because it doesn’t formally factor in travel or weather. A New York Red Bulls win over New York City FC in chilly March counts the same as an Orlando win over Vancouver in sweltering July. He hopes to improve the model soon, including offering the data publicly to fans so they can build their own formulas.

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So what’s the best betting tip? Pick the home team to win, no matter who’s on the field.

“Home advantage seems much more significant in MLS than it does in the Premier League and probably in most European leagues as well,” Szymanski said. “It is actually genuinely the case that home teams are much more likely to win.”

The model could change, especially as MLS teams shift foreign player spending toward younger prospects instead of big-name veterans. Good bets by front offices could lead to big jumps in teams’ Transfermarkt values.

For example, Los Angeles FC’s 23-year-old scoring ace, Diego Rossi, has seen his Transfermarkt value rise from $2.20 million when he arrived in MLS in 2018 to $22 million. The Union’s Kacper Przybylko was valued at $300,000 at the end of 2018, at age 22, and is now at $2.2 million.

It’s necessary to disclaim here that Transfermarkt values aren’t set by anyone official in the soccer world: not FIFA, team executives, agents, etc. As with any sport, a player’s real market value is what a team is willing to pay for him.

But taken in aggregate, the Transfermarkt database makes for a reasonable picture of the global soccer economy. Szymanski’s endorsement isn’t just anybody’s.

He also endorses the easiest way to create more variance in Transfermarkt values: if MLS loosens its rule book and lets teams spend more money.

“We can argue whether this is [morally] right or wrong, but MLS is clearly afraid of dominance by some limited number of teams if you allow free spending,” Szymanski said. “Maybe that would create an unbalanced competition, which would undermine interest. ... But in terms of success for a television audience, something which undermines the home-team advantage, however you did it, might not be a bad idea because it would then create a more attractive TV spectacle.”

That’s a formula any fan can understand.

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