Over the years, Bill Petti has done some fascinating research on hitter volatility. He recently updated that work at the new Hardball Times. I strongly recommend taking a look. You can follow Petti on Twitter @BillPetti. Hopefully he’ll now forgive me for shamelessly stealing his work for fantasy purposes.
Before we dive into Petti’s work and how it applies to fantasy baseball, let’s define volatility. In finance, volatility refers to variation in price over a period of time. A stock that sees frequent fluctuation of price is considered to be more volatile than a stock with very little price fluctuation. In fantasy baseball, we can replace price with category production or points. Player A is more volatile than Player B if his day-to-day performance is more varied.
Petti’s research is in day-to-day volatility, which differs from streakiness. As fantasy owners, we know that Jay Bruce is one streaky mofo guy. He’ll put up 20 excellent games followed by 30 atrocious games and he’s been doing it since the day he entered the majors. By Petti’s measure, Bruce is only four percent more volatile than league average over the last three years. That’s (probably) because he’s not measuring these long term fluctuations.
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