OPS Is Flawed, We Can Do Better

Last night I was watching Bill James’ fantastic 60 minutes piece when I asked myself a question. Why haven’t more people moved past on base plus slugging? Recently I have been reading “The Book”, which is basically a handbook to baseball written using historical baseball statics and sabermetrics. Early on the authors bring up a very interesting point. When people in the sabermetric community discovered that  the flaws in both OBP and SLG were equivalent to the strengths of the other statistic they decided to add them together. Although this definitely helped it still didn’t do the job perfectly.

The main issue with OBP is that it only takes into consideration weather a player reached base or not. Now this is a very useful tool, however it fails to consider the value of an extra base hit. SLG only takes into consideration total bases per at bat. It’s a very useful statistic however It does not take into consideration how incredibly more valuable anything is than an out. Where OBP will tell you how often a player managed NOT to make an out, SLG will not. A guy who reaches base once and gets 1 home run is not as valuable as a guy who walks 4 times. SLG would value both as equal.

Now combining the statistics to take into account both failure to make and out, and success at reaching multiple bases, should create a perfect statistic right? Wrong. OPS, or on base plus slugging, still fails in one significant way. It values each base as equal. This is entirely wrong. By looking at the run expectancy before, and after, and event on average through major league history we can see that certain base are more valuable than others. For example, the difference between a single and an out is greater than the difference between a single and a double. This is where a new statistic comes in, wOBA (or weighted on base average).

wOBA is a significant improvement of OPS. Instead of using total bases to value each event, for example saying a home run is 4 times as valuable as a walk, wOBA takes the actual run value of each event and then multiplies it by the number of times that event takes place. It then divides the number by plate appearances to get the true value a player contributes to his team each plate appearance. This also takes into account the value of anything over an out as an out lowers your value and anything else raise it. wOBA is the perfect combination of OBP and SLG that we have all been waiting for. Such a statistic is sabermetric gold. The exact formula at the time of the publication of “the Book” is:

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