Defense-Independent Pitching Statistics
Defense Independent Pitching Statistics (DIPS) are a subset of pitching metrics designed to measure a pitcher's ability using only outcomes that do not involve fielders: home runs allowed, strikeouts, hit batters and walks.
The theory behind DIPS is that there is little to no difference between the abilities of various Major League pitchers to influence the rate of hits against them on balls put into the field of play. In other words, defense-independent statistics such as walks, strikeouts and HR allowed are determined almost entirely by the pitcher's ability level. But defense-dependent statistics, such as the rate of hits allowed on balls put into play, are almost entirely the result of luck and the skills of the defensive players on the field.
Voros McCracken was the first researcher to publicly outline this effect, posting his findings to an internet message board (rec.sport.baseball) in 1999 and publishing an article on the topic for Baseball Prospectus in 2001. Before McCracken, even the most orthodox of sabermetricians believed that pitchers had varying abilities to prevent hits on balls in play. But McCracken examined pitchers' Batting Averages allowed on Balls In Play (BABIP), and found that there was essentially no correlation between a pitcher's BABIP from one season to the next, suggesting that factors beyond a pitcher's control (whether they be his defensive support or just luck) were mostly responsible for his rate of hits allowed on balls in play.
This finding was highly controversial, even in sabermetric circles. Later studies found that certain types of pitchers, including knuckleballers and extreme ground-ball inducers, did in fact have some consistent ability to suppress BABIP. But for the majority of pitchers, a combination of strikeout rate, walk rate and HR rate is more predictive of future ERA than past ERA itself.
The concept of "Fielding Independent Pitching", or FIP, was derived from DIPS.
- Dan Basco and Michael Davies: "The Many Flavors of DIPS: A History and an Overview", The Baseball Research Journal, SABR, Vol. 39, Number 2 (Fall 2010), pp. 41-50.