Advanced Stats 101: ERA+ and OPS+
We are going to start by explaining ERA. ERA is the average amount of earned runs a pitcher gives up over 9 innings (which I assume that most, if not all of you know). It is calculated by the following equation:
(9 * ER / IP). Its a simple stat, that has been around for many years, and has widely been accepted as “the” stat when judging pitching. What it does not do, however, is take into account the effect a ballpark has on a pitcher’s performance, or give us an average. For example, if Colby Lewis faced the Mariners in Wrigley Field and then pitched the same game against the same team in Dodger Stadium at night, would the outcomes be the same? Probably not. That’s a hypothetical, obviously since Colby could not duplicate the exact same pitches and the hitters would react differently, but you get the idea. What ERA+ does, is to average the ERA of a player against the league to give us the “average” pitcher. The equation is this: 100*(league ERA/the player’s ERA). What does this mean? It means that the “average” pitcher will have an ERA+ of exactly 100. ERA+ gives us a baseline or starting point to measure a pitcher against the league. Lets look at Derek Holland to give you a better idea.
|.||Derek Holland||Games||Innings||Hits||Earned Runs||ERA||ERA+|
OPS+ (On Base plus Slugging, Ballpark Adjusted)
OPS+ works much the same way as ERA+, but for hitters. It gives us a starting point to judge a player, by giving us the average. Let’s start with a quick tutorial of OPS. It’s on base percentage plus slugging percentage. That’s it, pretty simple. Any hitter with an OPS above .900 would be put into the “great” category. The OPS+ formula is:100*[OBP/lg OBP + SLG/lg SLG – 1]. The same with ERA+, 100 is the league average, and that is our “zero” point for looking at a player’s performance. Again, we’ll show you a player’s stats to help you get an idea. Here’s Adrian Beltre:
Next week, Advanced Stats 102. It will be all about pitching with RAR, FIP,xFIP, and my personal favorite Gsc.