In this paper, the new postseason format from 2015 season of J1 League, the top division of professional football in Japan, is simulated and analyzed statistically. Official regulation defines that the new postseason from the 2015 season consists of five teams selected by different principles — the top three teams by total season points, and the winning teams of the 1st and 2nd half of the season.
The simulation results concludes that there are overlaps within these five teams very frequently, therefore the postseason tournament will be held with 3, 4, and 5 teams (i.e., without any overlaps) with probability 62%, 35%, and 3%.
The result is obtained by using numerical simulation of 105 seasons. The goal scoring model is based on the results in 5 years (from 2010 to 2014 seasons), and is constructed by regression analysis technique.
This result clarifies that the new postseason format is inherently one-stage, NOT two-stage as officially defined, format because the selection condition for the postseason tournament is not designed correctly.
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