The major league baseball postseason is often referred to as a “crapshoot”, but is there any method to the madness that ends with a World Series champion? Are teams with a better record more likely to win in October, or is run differential a better barometer of postseason success? What about teams that are hot entering the playoffs, or those who performed better against stiffer competition in the regular season? Let’s take a look.
Regular Season Record
Since 1901, there have been 281 post season series, and the team with the better record has won only 53% of them. By individual series, only the ALCS has seen the better team emerge victorious more than 60% of the time. The same pattern also holds for more recent results. Since 1995, the team with a better record has won the ALCS 63% of the time, but the overall outcomes have been a coin flip.
Postseason Series Won by Team with Better Regular Season Record, 1901-2013
Note: Bars represents percentage of teams with a better regular season record that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
Post Season Series Won by Team with Better Regular Season Record, 1995-2013
Note: Bars represents percentage of teams with a better regular season record that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
Better is a relative term, but a one or two game difference over 162 has little meaning. In order to avoid that conflict, series results were grouped into winning percentage ranges. Using this approach reveals that as the differential widens, the better teams tends to be more successful. In fact, at the extreme parameter (winning percentage difference greater than 0.100), the percentage is 81%, albeit in a more limited sample of 16 qualifying series.
Rate of Postseason Series Success by Teams with Better Regular Season Record (Based on Defined Differential Ranges), 1901-2013
Note: Bars represents percentage of teams with a better regular season record (in defined ranges) that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
Pythagorean Record
Comparing Pythagorean records is a little more predictive than actual records. Over 58% of all post season series have been won by teams with a better expected winning percentage, and, this time, the ALCS is joined by each league’s LDS with a rate above 60%.
Post Season Series Won by Team with Better Pythagorean Record, 1901-2013
Note: Bars represents percentage of teams with a better Pythagorean record that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
Once again, looking at aggregate numbers can be misleading, so Pythagorean record ranges were used. Interestingly, expected winning percentages were more predictive at the lower end of the scale, but, at the highest parameter, teams with a better actual winning percentage were more successful.
Rate of Postseason Series Success by Teams with Better Pythagorean Record (Based on Defined Differential Ranges), 1901-2013
Note: Bars represents percentage of teams with a better Pythagorean record (in defined ranges) that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
When only considering those series in which one team had both a better actual and expected record, the overall rate of success for the better team actually declined a bit. However, at larger differentials, the better team was increasingly triumphant. When the gap was greater than 0.050 in both regular season and Pythagorean winning percentages, the team with the higher rates won 63% of the series. However, at differentials of 0.075 and 0.100, the better team’s success rate was 84% and 80%, respectively.
Rate of Postseason Series Success by Teams with Better Regular Season and Pythagorean Record (Based on Defined Differential Ranges), 1901-2013
Note: Bars represents percentage of teams with a better Pythagorean and Regular season record (in defined ranges) that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
Postseason Series in Which One Team Had Pythagorean/Regular Season Record Advantage of 0.075 or Greater, 1901-2013
Note: Red shading represents “worse” team that won the series. Blue shading represents only team in division series era to have 7.5% advantage in all three postseason series.
Source: baseball-reference.com and proprietary calculations
Better Record Against Other Postseason Teams
How teams perform against fellow playoff combatants seems like an intuitive barometer of October success. However, this often cited statistic seems to have little predictive value. Because the number of games against postseason teams was limited to LCS opponents prior to the wild card era, only series played since 1995 were considered in this analysis. Over this period, only 52% of all series were won by the team with a better record against postseason-level competition, although the ALDS and NLCS did approach 58%.
Postseason Series Won by Teams with Better Record Against Postseason Opponents, 1995-2013
Note: Bars represents percentage of teams with a better record against postseason entrants that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
Once again, this criteria was also analyzed based on relative performance ranges, but with an addition wrinkle. Instead of comparing all series to the difference, a control sample of matchups featuring teams with similar overall win rates was used. In this cohort, teams with better records against playoff opponents improved to a 54% success rate, although the ALDS boasted a more pronounced rate of 68%. However, there was no discernible pattern based on differences in winning percentage against playoff teams when regular season records were relatively even.
Postseason Series Won by Teams with Better Record Against Postseason Opponents (Involving Teams with Similar Regular Season Records*) By Series and Differential Ranges, 1995-2013
*Only includes series between two teams with winning percentage differentials no greater than 0.025.
Note: Bars represents percentage of teams with a better record against postseason entrants that won a playoff series. Number labels above aggregate categories represent total series played.
Source: baseball-reference.com and proprietary calculations
Better Final Month Record
The baseball season is a marathon, and some teams don’t hit their full stride until just before the finish line. Does the momentum gained in September carry into October? Based on the results of the first post season series played in each year, the answer is no. In the 128 first round series (excluding the one-game wild card play-in) since 1969, the victor has had the better final month (September/October) exactly half the time. However, when once again only considering those series featuring teams with similar overall regular season records, the impact of a hot final month is weakened even further. Among the 61 series that qualify, only 27 were won by the team with the better September record. What’s more, in the seven series that featured a greater than 0.200 difference in final month records, only three were won by the hotter team.
Initial Postseason Series Performance Based on Record in the Final Month, 1969-2013
*Only includes series between two teams with winning percentage differentials no greater than 0.025.
Note: Includes only LCS from 1969 to 1995, excluding 1981, and LDS for 1981, 1995-2013. Better refers to team with better record in final month (September/October).
Source: baseball-reference.com and proprietary calculations
Being hot before the postseason has little bearing on October success, but regular season, Pythagorean, and playoff opponent records do have some predictive value, particularly when either or all three involve an extreme difference. This October, there aren’t any potential series that would fall under the “extreme” characterization (although Angels vs. Royals and the Nationals against either N.L. wild card will feature regular season and Pythagorean differentials of 5%), so history can provide little help predicting this postseason. And, that’s exactly how major league baseball likes it. With competitive balance comes even more uncertainty in the postseason, making October the crapshoot many assume it to be.
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