Archive for October, 2016

The Beginner’s Guide To Understanding Descriptive and Predictive Stats

Baseball statistics are designed to answer questions. Some questions are simple, such as “who reached base most often in 2016?” while others are more complicated, like “who was the best base runner in the American League?” Statistics allow us to gather up data points from individual events and summarize them in ways that are easy to understand.

Different statistics answer different questions and therefore have different uses. You can’t figure out who the best hitter is solely by looking at his batting average. Batting average tells you something, but batting average itself answers a very specific and limited question. Over the years, we’ve attempted to expand the statistics we use to better capture the game we love. Instead of batting average, we moved to OBP, then OPS, then wOBA, and so on. The key is to decide on your question and then find which available statistic(s) best answers that question.

One issue that comes up regularly is whether a statistic is predictive of the future or merely descriptive. You’ve likely heard that FIP is a better predictor of future ERA than current ERA. For this reason, many people believe that FIP was designed as a predictive statistic. As I discuss here, that is not accurate, but the perception persists because FIP is useful for prediction.

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