base besides a hit. Conversely, on-base percentage (OBP), takes base on balls ("walks") and hit-by-pitches into consideration. Another issue with the traditional measure of the batting average is that it does not distinguish between hits (i.e., singles, doubles, triples, and home runs) and gives each hit equal value. A measure that differentiates among these outcomes is the slugging percentage (SLG). To calculate the slugging percentage, the total bases of all hits is divided by the total number of times at bat. Stephen Jay Gould proposed that the disappearance of .400 batting average (last achieved in MLB by Ted Williams in 1941) is actually a sign of general improvement in batting. This is because, in the modern era, players are becoming more focused on hitting for power than for average. Therefore, it has become more valuable to compare players using the slugging percentage and on-base percentage over the batting average. These two improved sabermetric measures are important skills to measure in a batter and have been combined to create the modern statistic on-base plus slugging (OPS). OPS is the sum of the on-base percentage and the slugging percentage. This modern statistic has become useful in comparing players and is a powerful method of predicting runs scored from a certain player. Some of the other statistics that sabermetricians use to evaluate batting performance are weighted on-base average, secondary average, runs created, and equivalent average. Pitching measurements The traditional measure of pitching performance is the earned run average (ERA). It is calculated as earned runs allowed per nine innings. Earned run average does not separate the ability of the pitcher from the abilities of the fielders that he plays with. Another classic measure for pitching is a pitcher's winning percentage. Winning percentage is calculated by dividing wins by the total number of decisions (wins plus losses). Winning percentage is also heavily dependent on the pitcher's team, particularly on the number of runs it scores. Sabermetricians have attempted to find different measures of pitching performance that exclude the performances of the fielders involved. One of the earliest developed, and one of the most popular in use, is walks plus hits per inning pitched (WHIP), which while not completely defense-independent, tends to indicate how many times a pitcher is likely to put a player on base (either via walk, hit-by-pitch, or base hit) and thus how effective batters are against a particular pitcher in reaching