The Deep Dive
Before I dive into the Atlanta Braves bullpen, I need to explain SIERA, DRA, and why I’m using ERA- and DRA- instead of ERA+ and DRA+.
Warning, boring details that might improve understanding ahead.
If you are among the well-informed, who understand ERA+ and –, SIERA, and DRA + and –, feel free to leap forward to the next page. I promise those who stay I’ll keep it pithy.
Skill-Interactive ERA (SIERA) tries to show the skill level of this pitcher. It’s a step up from FIP, which only looks at the three true outcomes by adding ball-in-play outcomes.
Deserved Run Average (DRA) goes farther than the SIERA by including and adjusting for park, opponent, and, when helpful, framing, temperature, and pitch type as well.
Pluses and minuses in stats, oh my!
Baseball-Reference created ERA+, and everyone said cool, or something some interested in easy-to-understand stats says a new one they like appears. Across the road and down the hill, Fangraphs published ERA-.
Being a simple guy, I assumed – yes, I know what happens when you assume something – they were simply different ways of saying the same thing. They sort of are; both are ways of looking at a pitcher’s performance, but not the way I was interpreting the numbers.
On the off-chance someone is making the same kind of error, I thought it wise to explain what I learned ten years too late. Put as simply as possible, one is the inverse of the other:
- ERA+ is designed to show how the league compares to the pitcher. It is scaled to 100 for convenience but is not a percentage.
- ERA- is designed to tell you how the pitcher compares to the league. It is scaled to 100 as well, but each point above or below 100 represents a percentage point.
For example, Baseball-Reference shows A.J. Minter with a 2.09 ERA and a 197 ERA+. If you flip to their advanced pitching stats, you’ll see he also has a 51 ERA- making his ERA 49% better than the league.
Both stats have their uses, but most of us want to know how our pitcher looks compared to the league, which makes minus stats like ERA- and DRA- more informative.
Now, I return you to your regularly scheduled post in progress.