Add new comment

That's a key point that I hadn't been appreciating nearly enough.  I need to think about it.  A lot.
..........
I don't know whether it outweighs the question of the problem's complexity -- perhaps we're talking 80% about the same thing.
For example, if you're trying to predict the number of home runs that Jason Bay is likely to hit this year - the 50th percentile, assuming a total of 450 AB's, suppose I use PECOTA's model and come up with 11 homers.
How do I know that PECOTA is NOTICING all the variables that could affect the outcome?  There's a certain chance that playing in New York deflected his career arc (as Safeco did Beltre's).  Where is that in PECOTA, or in your or my quantitative model?
There's a certain chance that hyper-intelligent, soft-spoken people (like Bay is) see this effect amplified.  Maybe he's a sensitive personality (I think he actually is) and if you normalize for "sensitive people who spiral down in NY" then his chances to hit 20+ homers change.
There's a certain chance that Bay is an AL player, whatever that is.  Did we notice that variable?
The way the variables INTERACT is incredibly complex.  For example, maybe an Omniscient Computer would compare the SINE WAVE of Bay's career EYE to his career ISO and find that, when the sine waves intersect at moments A, B, and C, his chances for an age-34 bounceback are deflected.
............
The reason I mention, is because am familiar with just how tough it is to capture these variables from a chess-algorithm standpoint.  In fact you cannot teach a computer to play chess well, using abstract or general principles; it has to use brute force calculation of all possible outcomes (not available here, obviously).
I'd be very interested in your comments, Kelly.  How do we ever become confident that we have noticed and captured the real-world variables that impact Bay's results? 
..................
I'm taking psychology from one of the country's most accomplished PTSD counselors right now.  Am learning a lot, but am becoming more and more convinced that you can't predict people.... :- )
Obviously, we know some things.  We know that one hundred 34-year-olds, as a group, are a worse bet than a hundred 27-year-olds.  Sigghhh...