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  • Era/xera

    I know you guys at BBHQ answer this question often, but I can't find the link anywhere to explain it (still getting used to the new format...which I like btw).

    Anyway...the question.

    Please explain the difference again between ERA and XERA in the pitching portion of the player projections.

    Which is the better category to use for a good gauge of what to expect this year?

    Thanks in advance.
    "Get your a** back there! The only thing you know about pitching is that you can't hit it". ~Bob Gibson to his catcher Tim McCarver when McCarver approached him on the mound.

  • #2
    a little help

    xERA is a much better predictor of future ERA, or at least a better indicator of past skills. Oftentimes a pitcher can get very lucky or unlucky with respect to hit% or strand% giving him a much higher/lower ERA than he desreves for the skills he's displayed. xERA tries to account for these swings and can get you some excellent deals in your draft. For instance Cliff Lee finished with a 5+ ERA last year but alot of this was due to bad luck, while still displaying excellent skills as indicated by his much lower xERA. You should read the forecasters toolbox link to explain a lot of this stuff more clearly. good luck


    • #3
      I don't think xERA gets predicted. Or at least in terms of forecasting, I believe ERA and xERA are one and the same.

      What xERA does, is LOOK BACK on a given set of pitching statistics and calculate what the ERA should have been after luck (good or bad) is removed from the equation.

      EDIT: I just went and looked at projections and they include both ERA and xERA and they are different from each other so please ignore my ignorant post


      • #4
        You can read more about xERA in the glossary. Here's the link -


        • #5
          When thinking of xERA, I highly recommend looking at Burnson's formula so you really understand the components. It is so logical it is sickening. It uses the three most predictable and relevant pitcher skills (strikeouts, walks, and groundball/flyball allowance) to determine an expected strand rate (which has as strong a correlation with actual strand rate as may be possible without using overlapping variables), uses a normalized level of home runs per flyball allowed (HR/FB) to determine an expected HR rate, and then applies the expected strand rate to the expected number of baserunners (again based on BB rate and league average hit rate on balls in play) to determine how many total runners will score in the number of innings pitched. Thus expected ERA.

          xERA can and almost always will differ from actual ERA historically, and can and almost always will differ from projected ERA because the xERA formula does not account for park factors, team defense, or a pitcher's magical ability to have a lower- or higher-than-average hit rate on balls in play, all of which affect ERA. If you want to get fancy, you can manipulate the xERA formula to account for these things, though in most cases it doesn't change the results dramatically so I wouldn't recommend the effort.

          I noticed the actual xERA/xS% formulas aren't available on the site (not sure why, so I won't post them in case it is intentional; the glossary only has the old xERA formula), but they are in the 2005 Forecaster.


          • #6
            So if one were able to only take ERA or xERA into his draft for speculation on the pitcher's performance in 2005, which would you rely most on?

            I realize and understand the value of using the range between the two...but which way would you most lean?
            "Get your a** back there! The only thing you know about pitching is that you can't hit it". ~Bob Gibson to his catcher Tim McCarver when McCarver approached him on the mound.


            • #7
              I would use the actual ERA projection, not the xERA projection. Think of xERA as "potential" (in a good or bad way). Jose Contreras' or Aaron Harang's projected ERA will likely be higher than their projected xERA, and I would bid based on the ERA with the understanding that the xERA is a possibility if things go right.