Regular-Season Performance Versus Post-Season Success - Part 2

In my last post, I looked at the correlation between regular-season win totals and post-season success and found no clear association between the two.  Teams seemed to have equal likelihood of winning their divisional series, winning a pennant and winning the World Series regardless of their win totals in the regular season.

A better measure than wins of the dominance of a team is run differential (runs scored minus runs allowed), so I'm going to do a similar analysis using that.  Here, the 128 playoff teams between 1996-2011 are divided into approximately equal-sized groups (called quartiles) based on run differential.  The first quartile contains the bottom 25 percent of teams, that is, teams with a run differential of 77 or less.  The second, third and fourth quartiles include teams with run differentials of 78-114, 115-149 and 150+ respectively.

Table 1 shows the relationship between run differential and post-season performance.  The first rows tell us the following:  33 teams had run differentials of 77 or less, 16 (48%) triumphed in the divisional series, 7 (21%) won the pennant, and 5 (15%) were world champions.  As we saw with wins, the percent of teams winning in the first round of playoffs does not change very much across quartiles. 

However, teams with run differentials of 150 or more were almost three times as likely as the 77 and under group and nearly twice as likely as the middle quartiles to win the pennant.  The 150+ quartile was also most likely to win the World Series, but not by much: 18% for 150+ versus 15% for 77 and under. The results are not statistically significant, in part because 16 years is not a large sample. 

Table 1: Post-Season Performance by Regular Season Run Differential

Regular Season  Run Diff	Teams	Divisional Series	Pennant	World Series
<= 77	33	16(48%)	7 (21%)	5 (15%)
78-114	33	16 (48%)	10 (30%	3 (9%)
115-149	29	13 (45%)	4  (31%)	2 (7%)
150+	33	19 (58%)	11 (58%)	6 (18%)

Data from Baseball1.com

In Table 2, the teams are divided into groups according to where they finished in run differential among the four teams in their league each year.  Here, we see stronger evidence (although still not statistically significant) of more dominant regular-season teams doing better in the post-season.  The top-ranked teams had a higher likelihood than the bottom-raked teams of winning the divisional series (66% versus 47%), pennant (38% versus 19%) and World Series (22% versus 9%).

The results of this analysis are more in line with what you might expect.  The less dominant teams do have a decent chance of post-season success. Indeed, nearly half (47%) of the fourth-ranked teams got by the first round of the playoffs.  Additionally 7 of the 16 World Series winners ranked third or fourth in run differential.  Similarly, the strongest teams can fail in the playoffs - about a third (34%) of the top-ranked teams did not get past the first round.  However, we are seeing some evidence that teams with the best run differential do have a somewhat better chance at playoff success.   


 Table 2: Post-Season Performance by Regular Season Run Differential Rank

Regular Season Run Diff	Teams	Divisional Series	Pennant	World Series
Fourth	32	15 (47%)	6 (19%)	3 (9%)
Third	32	16 (50%)	7 (22%	4 (12%)
Second	32	12 (38%)	7 (22%)	2 (6%)
First	32	21 (66%)	12(38%)	7 (22%)

Data from Baseball1.com