Comparing individual team run production

Or, The 2010 Mariners: How Bad Were They?

In earlier posts, I used the statistical software R to plot the trends in league average run scoring since 1901. This was the first step to answering other questions I had on my mind:

1. How poor was the offensive performance of the 2010 Seattle Mariners?
2. Are they showing any signs of improvement?
3. And how can I use R to tabulate the data to answer these questions?

So, to answer Question #1.  It is well-established that the 2010 Mariners were not very good, at least offensively. (For fans of the team the well-deserved Cy Young award won by Felix Hernandez is surely the highlight of the season.) But I wanted a form of relative measure that would be comparable across time, to accommodate the various fluctuations in run scoring that were the subject of that earlier post.

As I started into this, the first decision was to draw a line in the historical record. I opted to use the eras described in Bill James' "Dividing Baseball History into Eras" article (behind a pay wall – but chances are if you're reading my blog, you already a Bill James subscriber):

• Era 1 (The Pioneer Era), 1871-1892 
• Era 2 (The Spitball Era), 1893-1919 
• Era 3 (The Landis Era), 1920-1946 
• Era 4 (The Baby Boomers Era), 1947-1968 
• Era 5 (The Artifical Turf Era), 1969-1992 
• Era 6 (The Camden Yards Era), 1993-2012

Based on these groupings, I opted to use the range of seasons 1947-2012 inclusive. This yields 1,580 team seasons of National League and American League baseball.

The second step was to calculate a runs per game (RPG) for each team, by year. This corrects for the longer regular season in the post-expansion period, the strike-shortened seasons, and will give us a common denominator to compare the results so far in 2012.

To do this, I accessed the 2012 edition of the Lahman database. Once I had downloaded and extracted the comma-delimted version of the files, I read the "teams" file into R.

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