This season, Italian side Juventus fulfilled an extraordinary achievement. Not only did they win the Italian league, they did it without losing a single game on the way. But exactly how extraordinary is this achievement?
Well, after clicking through all final league tables of the 5 big European leagues (England, Spain, Italy, Germany, France) at Wikipedia, I found that unbeaten seasons is a rather new phenomena. It happened twice in the early thirties in Spain, when the league only consisted of 10 teams, making the likelihood of an unbeaten season much higher than today, where the league consist of 20 teams (Exactly how much more likely is not interesting right now). After these two occurrences, the remaining 4 unbeaten seasons in the 5 leagues are to be found from the late seventies and up to this season.
Just looking at the table, it looks like it wasn’t a coincidence that the unbeaten season should appear in Italy, but the observations are very few, so let us assume that unbeaten seasons have same probability of occurring in all 5 leagues. Then, counting from the 1946-1947 seasons (1963-1964 for Germany) until the 2011-2012 seasons, the estimated likelihood of an unbeaten season in each league is 4/(66*4 + 49) = 0.0128. That is, in approximately 1 of every 78 league seasons, we will experience an unbeaten season, or we will experience 1 unbeaten season every 16 year across all 5 leagues.
Say Italy is special, in the matter, that unbeaten seasons are more likely in Italy than in the other 4 leagues, then the estimated likelihood of an unbeaten season each year in Italy is 3/66. That is, every 22nd year an Italian team will make an unbeaten season.
Well, after clicking through all final league tables of the 5 big European leagues (England, Spain, Italy, Germany, France) at Wikipedia, I found that unbeaten seasons is a rather new phenomena. It happened twice in the early thirties in Spain, when the league only consisted of 10 teams, making the likelihood of an unbeaten season much higher than today, where the league consist of 20 teams (Exactly how much more likely is not interesting right now). After these two occurrences, the remaining 4 unbeaten seasons in the 5 leagues are to be found from the late seventies and up to this season.
| Country | Season | Team | W | D | L | Placement |
| Italy | 2011-2012 | Juventus | 23 | 15 | 0 | 1 |
| England | 2003-2004 | Arsenal | 26 | 12 | 0 | 1 |
| Italy | 1991-1992 | Milan | 22 | 12 | 0 | 1 |
| Italy | 1978-1979 | Perugia | 11 | 19 | 0 | 2 |
Just looking at the table, it looks like it wasn’t a coincidence that the unbeaten season should appear in Italy, but the observations are very few, so let us assume that unbeaten seasons have same probability of occurring in all 5 leagues. Then, counting from the 1946-1947 seasons (1963-1964 for Germany) until the 2011-2012 seasons, the estimated likelihood of an unbeaten season in each league is 4/(66*4 + 49) = 0.0128. That is, in approximately 1 of every 78 league seasons, we will experience an unbeaten season, or we will experience 1 unbeaten season every 16 year across all 5 leagues.
Say Italy is special, in the matter, that unbeaten seasons are more likely in Italy than in the other 4 leagues, then the estimated likelihood of an unbeaten season each year in Italy is 3/66. That is, every 22nd year an Italian team will make an unbeaten season.
