A splitting headache
Jun 30, 2008
Todd B didn't like this chart showing the correlation between baseball team salaries and their win-loss records.
A few problems are in plain sight:
- Most importantly, putting a second set of logos next to the salaries column would really help
- Unclear why the lines should be of varying widths
- Winning percentage is more telling than win-loss, especially in the middle of a season when there is a slight imbalance in total games played
- the spread of salaries is so wide (10 times) that reducing the numerical scale to rank scale meant a big loss of information
- Each column is sorted by its own metric while the most important sorting variable should be the slope of the lines (i.e. the cost per win)
The interactive feature of individual plots for each day (control bar at the top) of the baseball season is something of a gimmick. Props though for realizing that the first few days of the season don't tell us anything. There really is little use for investigating this correlation on a day-by-day basis. Particularly when the salaries are given in aggregate.
On the diagram, the blue lines represent teams such as the Devil Rays and Arizona that had better winning records than their salaries would suggest. Red lines display those teams spending more money than their records would suggest. The steeper the line, the best/worst the team's cost efficiency.
With so many long steep lines in both colors (directions), one might posit that a negative correlation may exist between salary level and winning record.
The following scatter plot suggests otherwise:
The correlation between salary and winning is very weak. If one were to fit a linear model, it would show that the higher-salaried teams generally were doing slightly better (black line). The Yankees were sufficiently outside the range in salaries that I didn't include them in estimating the line. (However, as the chart shows, the line in fact estimated the Yankees winnning percentage really well.)
Teams above the line are performing better than their salaries would lead us to believe.
Reference: Ben Fry's baseball salary page