I want to note that's not the only way to do it. He's assuming a somewhat normal distribution of talent, such that the 12th best shortstop isn't freakishly good or freakishly bad. Lets say for some reason there are 11 great to good to bad shortops, and then our 12th shortstop hits .100 with 5 RBI and 5 runs.
If the really awful 12th guy has a sum of his standard scores of like -50, then that'll screw up the calculations pretty badly. While it's certainly correct to say everyone else's value above replacement is now 50+their own value, it's not so helpful when comparing positional values.
Now this is more of a hypothetical concern. In my experience there's rarely a freakish dropoff at the low end. However, when I run my own values, what I do sometimes do is an average of the bottom end. So again, in a 12 team league, I average the production of 11, 12, and 13 to generate an approximation of replacement level.
You can also dispose of the entire replacement level concept. To create positional adjustments, just sum up the 12 best guys at each position, and then measure everyone by value above average instead of value above replacement. Tulo is worth 8 units, the average of the top 12 shortstops is worth 3 units, so then Tulo is 5 units above average. Our 12th guy, with a value of -5 meanwhile is 8 units below average.
Neither system is "correct." I would just use whichever one seems more intuitive to you on this point.
Feel free to e-mail me at [my username]@gmail.com if you have any other questions. I can help run you through the setup he's got there, plus I've got some ideas he doesn't cover, and to my knowledge, no public site cover (which are absolutely critical for fantasy baseball evaluations, but curiously aren't for basketball).
I've given the idea of valuations a ton of thought, but I don't have the coding skill to create these systems myself. That's why I signed up for Baseball Mogul. Your integration with Yahoo/ESPN/CBS is spectacular, as is the ability to create daily projections/ease rankings. The Last Player Picked tool does a lot of stuff right, but they also make some mistakes and don't have your ease of use.
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