Just when you thought this blog was dead and buried, Matt Swartz comes riding to the rescue. At FanGraphs, he has a new five-part series on everyone’s favorite stat, SIERA. Because last time around, as Swartz trumpets, he and his partner in
stupidity crime, Eric Seidman, “didn’t totally appreciate why it worked.” And the name “skill interactive” was completely misleading, too. It’s not like you two devoted more than 10,000 words and its own five-part introductory series on Baseball Prospectus about it last winter. This time, though, Swartz has totally got this.
He isn’t shying away, though. He answers the questions SIERA-atics (like myself) have often asked, like, “Why aren’t there more terms in this equation?” To which he says, in Part Two, “Excellent question. I’ve added (BB/PA)^2, (SO/PA)*(BB/PA), a run-environment variable, and percentage of innings as a SP! And all only because they improve my RMSE!” Swartz even managed to flip the sign on one of the preexisting terms with no explanation why.
I don’t know anything about FanGraphs’ business, but bringing on Matt Swartz and letting him revamp SIERA has to be a waste of money. A one-percent improvement over xFIP would be valuable to a team, I imagine, but to the average fan, it’s worth zero. Maybe less than zero when it’s impossible to explain in English the rationale for the stat. (Though we’ll have to wait until Part Four to see the comparison between the two, I wouldn’t bet the improvement is close to one percent. And there’s always a good chance that the comparisons aren’t done correctly anyway.) So they’re paying Swartz to blather on about something pointless at best and wasting Dave Appelman’s time in having to add it to their database. The rich grandpa lives on.
Somewhat surprising to me is that the FanGraphs commenters are being uncharacteristically kind to Swartz and his Frankenstein stat. Baseball Prospectus commenters, less so.