It started with Sabathia and Sheets. Cain, Greinke, and Nolasco followed.  Most recently, Peavy has been discussed as a possible acquisition target for the Rangers this off-season.  Each of these pitchers is undoubtedly a better bet to pitch well in 2009 than anyone on the Rangers current 40-man roster.  However, each of these pitchers will come with a significant cost.  Signing either of the free agents will require the Rangers to use 20-25% of their annual payroll on a single player.  The four trade targets would likely require the Rangers to give up 3-4 quality prospects or young, inexpensive major league players.  Which begs the question – What is the value of an ace?  Or put another way, does having a legitimate #1 starter affect a team’s chances to contend for a playoff berth?

To address the question of whether an ace increases a team’s chances of reaching the playoffs, I used data from the past five seasons to determine the correlation between teams with aces and teams that made the playoffs.  Identifying the aces was a bit tricky since there’s not a clear definition for an ace.  I wound up selecting two classes of aces – those who have ranked among the top pitchers in their league for several seasons and those who ranked among the league leaders during the season being assessed.  The former group included pitchers like Halladay and Webb while the latter class included pitchers like Matsuzaka and Lincecum who have only recently ascended to acedom.

The Perennial Aces
To identify pitchers who are consistently among the league leaders, I used ERA+ to rank AL and NL starters with at least 100 innings pitched for the 2003-2008 seasons.  20 pitchers finished in their league’s Top 20 in at least three of the six seasons that I evaluated (Halladay, Sabathia, Buehrle, Clemens, Cook, Hamels, Kazmir, Lackey, Lowe, Oswalt, Santana, Schmidt, Sheets, Smoltz, Peavey, Hudson, Carpenter, Mussina, Webb, and Zambrano).  The primary problem with this list is that injuries and occasional bad seasons make these perennial aces less than stellar in some years.  In fact, only Halladay, Santana, Oswalt, Webb, and Zambrano posted an ERA+ greater than 115 in each of the 6 seasons used for this analysis.  To account for this issue, I dropped pitchers from this list for the seasons that they pitched fewer than 100 innings or posted an ERA+ that was league average or worse.

Annual Leaders
The second group of “aces” used for this analysis included the ten starters who pitched at least 100 innings with an ERA+ that was among the top ten for the league in which they pitched.  There were ten different lists of annual leaders (2 for each league for each of the five years used in the study).  The annual league lists included pitchers from the perennial aces list as well as Greinke, Lincecum, Hernandez, Lee, Volquez, Lester, Guthrie, and others.

For each of the two groups of aces, I asked a simple question: What percentage of playoff teams and what percentage of non-playoff teams during the past five years had an ace on their staff.  One would assume that great pitchers or pitchers having great seasons would improve their team’s record and thus improve their team’s chances of making the playoffs.  If true, the net result would be that the percentage of playoff teams with aces would significantly outpace the percentage of non-playoff teams with aces.  Surprisingly, the percentage of playoff teams with at least one ace of either category only slightly outpaced the percentage of non-playoff teams with an ace on-staff for each of the five years used for the study (see below).  The average percentages for the five years for playoff vs non-playoff teams were 53% vs 49% for the teams with perennial aces and 60% vs 47% for the teams with annual leaders. 

                                                                         2004     2005     2006     2007     2008
Playoff teams w/perennial aces             37.5%    75%     37.5%    75%     37.5%
Non-playoff teams w/perennial aces      45%      45%      59%      30%      45%

Playoff teams w/annual leaders              50%     62.5%   50%     62.5%    75%
Non-playoff teams w/annual leaders      45%      50%      50%      45%      45%

These data reveal that having an ace is neither necessary nor sufficient for a team to make the playoffs.  Furthermore, it appears that having an ace on staff does not substantially improve a team’s chances to make the playoffs.  Because I was surprised by this result, I reviewed the records of teams that have the best pitchers in baseball in games started by their aces and compared it to the same teams’ records in games started by everyone else.  As noted in the table below, teams are better when playing behind great pitchers, but the difference is rarely sufficient to change a team's playoff fate.  Presumably, that is why there is only a slight enrichment of aces on teams who make the playoffs.

Team/Pitcher              Record in games w/ace    Record in other games    Overall
BlueJays/Halladay               21-13                                          65-63                     86-76
Angels/Lackey                       15-9                                            85-53                   100-62
Cubs/Zambrano                   20-10                                          77-54                     97-64
Astros/Oswalt                       20-13                                           66-62                     86-75
Mets/Santana                       22-12                                           67-61                     89-73

One compelling argument that has been made in favor of adding an ace is the benefit that a team receives when they make the playoffs.  Teams typically go to 4-man staffs and thus an ace has an opportunity to impact 25% or more of the games in a 5 or 7 game series.  Using the same five pitchers as above, is there data to support this argument?  Though the number of games for each of the pitchers is relatively small, there does not appear to be a particularly strong correlation between regular season dominance and post-season success (see table below).

Pitcher        GS     ERA    Record        Team Record
Halladay       0
Lackey          9      3.39       2-3                   4-5
Zambrano    5      4.34       0-2                   1-4
Oswalt          7      3.66       4-0                   4-3
Santana       5      3.97       1-3                   2-3

Curious about the regular season and playoff impacts of the six pitchers that have been the source of various Rangers fans’ obsessions?  Below are the 2008 regular season and career playoff records of Sabathia, Sheets, Cain, Greinke, Nalasco, and Peavy.

Player      2008 record w/ace    2008 record w/others    Playoff- Starts  ERA  Rec
Sabathia               22-13                                   ??                                         5     7.92   2-3
Sheets                  18-13                                 72-59                                     0
Cain                       14-20                                58-70                                      0
Greinke                 16-16                                59-71                                      0
Nolasco                21-13                                63-64                                      0   
Peavy                    12-15                                 51-84                                      2    12.10   0-2   

What is an ace worth?  An extra 3-5 wins per season for an average to above average team; less for a below average team.  If those 3-5 wins cost you two or three young players with all-star ceilings and/or 20-25% of your payroll, I have a hard time seeing how a smart, medium payroll team can justify the expense.