Accuracy of Projections?

awinters  4/10/2015 8:21 PM

The projections seem overall a little too good so as a test I totaled the rest of season projections for the entire league (all pitchers, not just top pitchers).  For the rest of season I am showing a total ERA of 3.55. This is compared to a 3.74 ERA for the entire league in 2014.  Shouldn't the projections for this season be roughly pegged to last season?  Is there a reason to think that ERA will improve that much?  In fact, there hasn't been a league wide ERA that good since 1976.  I haven't analyzed all the other stats in detail but I suspect there is similar total bias in favor of improved results.

Even more dramatically is the difference in the weekly projections.  When I run the projections for all pitchers for the next 7 days (4/13 to 4/19) I get a total ERA of 3.23.  I can concede that in a given day, especially opening day when we have mostly aces pitching, the ERA could be much different than average.  But over an entire week I would think this would roughly even out for the entire league so I am wondering why the ERA is so much better for a week as opposed to the entire season. Also, when I run for just SP during the week I get an ERA of 3.23 while RP pitchers have an ERA of 3.24 for the week -- almost the same. This contradicts the well established record that relievers will have a better ERA than starters.

I hope this isn't nitpicky but it impacts my analysis and I feel the need to make adjustments to the projections based on more realistic expectations.  Any explanation for my observations would be appreciated.

ken_admin  4/10/2015 8:48 PM

Thanks for the details.  I would expect the season ERA to be a little lower since we do assume good health for most players, and obviously, not everyone will accomplish that. A difference of 1.9 seems a little high so I'll see what a reasonable number would be.  I can check the short-term ERA numbers too and get back.

awinters  4/10/2015 8:55 PM

Thank you and I should add I think the projections are very accurate and helpful in terms of comparing players to each other, which is their primary usefulness.  I'm just wondering if I need to input a league wide adjustment but I figured I'd give you a chance to respond first.