There's No Place Like Home -- AL Edition

So here goes a second FanPost (the first one being The Eye of The Elvis).  I've taken a slightly more difficult topic, which neccessitated a slightly more technical approach, as well as slightly more tables and words to explain and answer the question (that having been said, I attempted to keep everything as organized and easy to read as I could).  Enjoy!  --JP

Introduction/Statement of Question:

As anyone who has watched a Rangers home game on national television knows, the commentators love to jabber about how the Rangers hitters enjoy a significant advantage when playing at home.  This isn't the exact topic I set out to examine, but instead it provoked me to answer a different question:  which team this year has played better at home, compared to their performance on the road?

 It's worthwhile to clarify the question here:  I don't want to study the best home teams here;  that would hardly be worth the trouble of writing a FanPost, since I could just glance at the home/road (or, if I wanted to take "luck" out of it and be a bit more precise, use the Pythagorean W-L formula for the home and road records).  Instead,  I want to find who plays the best at home, relative to how they play on the road. 

There seem to be a couple of ways to study this question.  The most simplistic (and perhaps least exact) method would be to subtract a teams home winning percentage from their road winning percentage.  This method would certainly give us a vague answer to our question.  A second would be the teams home/road split slashlines (AVG/OBP/SLG), yet this would make it difficuly to quantify our results.   I'd like to look at it from a more exact point of view:  in terms of runs scored/game and runs allowed/game:

Here are the runs scored and runs allowed per game stats for the American League at home, as of August 9th at the end of game play (sorry if it's a bit difficult to read, I had some formatting issues):

The Home Data:

The key stat here is the Differential/Game (given by RS/G - RA/G), which tells us the average scoring margin of the team's home games.  For instance, the Rangers score 1.37 more runs on average at home than their opponents.  The next table shows similar statistics for AL teams on the road:

The Road Data:

These two tables in themselves are enough to study individual teams on their own.  For instance, we can see that the Rangers are indeed a much better team at home:  they outscore their opponents by an average of 1.37 runs/game at home, contrasted with 0.39 runs/game on the road. 

We can further elucidate the differences and allow for easier comparison, however, by combining the results:  substracting the Road Differential from the Home Differential (call this "new" stat Total Home Advantage).  For example, the Total Home Advantage (THA) for the Rangers is .98, meaning that the Rangers' average run differential is .98 runs per game greater at home than on the road.  (**By "new", I mean that I created it based on the data I was using for this post; it's very possible that this or a very similar stat has already been devised.)  The THAs for the rest of the league are listed in the following table:

Combined Data (Total Home Advantage = Home Differential - Road Differential)

Tips for using/how to read the Total Home Advantage (THA) statistic:

Before going any further, here are some important features of this statistic, as a result of it's construction:

**the THA means that the team's average run differential is _____ more runs per game at home than on the road

**a negative THA means that the team is worse at home than on the road (in other words, better on the road)

**A THA near 0 indicates that the team's home/road differentials are virtually indistinguishable

**A higher Total Home Advantage does not necessarily mean that the team has been good at home or even a good team at all (see Seattle and their 1.43 THA, for example), merely that they have been that much better at home than on the road

 **A lower Total Home Advantage does not necessarily mean that the team has been bad at home or even a bad team at all (see Tampa Bay and their -.74 THA), merely that they have not been as good at home as on the road

 **THA is a measure of how the team has played in their home ballpark relative to how they have played elsewhere, not a measure of the ballpark itself (in other words, it's not a park factor)

Summary of results:

We can see that the top 4 teams are:  (1) Oakland, 1.97    (2) Detriot, 1.77    (3) Toronto, 1.61, (4) Seattle, 1.43.  This is interesting to me because all four of these teams play in pitcher's parks, and additionally none of these teams look to be serious contenders this year (so the teams that have played much better at home aren't even the best teams in the league, and in Seattle's case, one of the worst).

On the other hand, the bottom 4 teams are:  (1) Tampa Bay, -0.74    (2) Boston, -0.10   (3) Baltimore, -.01,   (4) LA Angels, 0.22.  This list was quite surprising, due to the fact that Tampa Bay over the last few years has played exceptionally well at home, and Boston is always touted for their homefield advantage at Fenway.  Of course, since THA measures performance at home relative to performance on the road, the home field advantage could very well still be there, and this could just be due to the fact that these two teams are playing superior baseball on the road as well.  It is also noteworthy that one of the worst teams in the AL makes the Top 4 list (Seattle), while one of the best teams in the league makes the Bottom 4 (Tampa Bay). 

Source used for data:  Baseball Reference