November 23, 2009
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Let’s do the time WARP!by Colin WyersOctober 23, 2009 Baseball Prospectus has a metric called Wins Above Replacement Player, which (ideally) should be a pretty straightforward proposition. But let's look at a few things. I have a collection of sortable WARP1 reports from October 9th, covering 1996-2009. How does it match up what's currently on the site? Currently, BPro says Vlad was worth 59.1 WARP1 in that timespan. Based on what was reported on the 9th, Vlad was worth 69.8 WARP1. Okay, so that's just one player. Let's try... Scott Rolen. 75.9 WARP1. A few weeks ago? 82.4. Nomah? 49.6 WARP1, compared to 59.0 WARP1 before. So what's going on here? Aggregate WARP1 per season has declined by roughly 150 over the past few weeks. That's right - nearly 150 wins per season have simply disappeared from Baseball Prospectus' website. Why? It seems that BPro has changed how they convert runs to wins. Before, they were using a scale where 8.2 runs = roughly 1 win. Now it's a lot closer to 9.2 runs per win. (For a fuller explanation, check out this discussion of the subject.) This is, by all accounts, good (it has the nice side effect of making individual player WARP sum up to team WARP, assuming a replacement level of .220 - we can have that conversation another time). Just one question - why hasn't BPro announced this change? Colin Wyers knows exactly how much of a nerd he is. He is very interested in hearing about any other concerns you may have; you can reach him by e-mail, and he will try his best to respond in a timely fashion. He also blogs at Statistically Speaking.
Colin Wyers said...
You flatter me too much, Nick. It may well be that I should leave the matter alone, but I seriously doubt “lunch money” is the reason. I really doubt that what I do here has much of an impact on what Baseball Prospectus does at all - if I am trying to be a bully I am doing very poorly at it. If I do ever get some lunch money (like if VORP ever stops valuing the walk incorrectly), then we can talk about it. (Or maybe I start going after breakfast and dinner money, too.) Posted 10/23 at 11:43 AM
DS1 said...
It’s not that they’ve changed. It’s that the data is worthless. If you check tomorrow, it will be a different number. And the next day and so on. I pointed out this problem to them in June and got absolutely no response. Posted 10/23 at 12:33 PM
JayT said...
I know earlier this year they changed they way their fielding stat FRAA is calculated, and it is used in calculating WARP, so I would guess that is what changed it. Posted 10/26 at 12:02 PM
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C’mon Colin, leave BPro alone. You already got his lunch money.