I've been trying to remember to link to the explanatory posts, but, of course, I forgot on the initial "Spec66" article. And, the esteemed Lonnie of MC (MarinerCentral.com, of course), asked for bit more background, and, obviously, he's entitled. Lonnie probably injects more names into the conversation than anyone.
So here goes.
"The Three Numbers" are based on two stats that I developed (the third one is a composite of the other two). I developed the stats because I concluded that strikeout rates were a huge indicator of which minor-leaguers went on to MLB success, and traditional stats didn't take strikeout rates into account.
They're just my view of what a useful indicator is, not an attempt to "solve baseball" into one set of numbers.
"Hitter's +/-" is a way of measuring the hitter's ability to "win plate appearances" by avoiding strikes and "pitcher's pitches," taking balls, and selecting "hitter's pitches." I consider it an "indicator" of OBP, not necessarily a predictor. But it's getting at the "reaching base" part of the game.
For pitchers, it's the reverse -- measuring the pitcher's ability to throw strikes and avoid balls while not serving up meatballs, and, generally, keep guys off the bases.
The full explanation of "Hitter's +/-" is here.
"Plausibility" is a way of measuring the hitter's ability to "produce" at the plate by measuring ability to hit the ball with authority and take walks while avoiding strikeouts. It is measured by the "necessary conversion rate" of "random-y" balls-in-play to "random-y" singles for a high OPS, based on actual home runs, extra-base hits, walks and strikeouts. If a hitter needs a very low conversion rate of balls-in-play to "fall in," then he scores well. I consider it an "indicator" of SLG, or at least of the ability to produce offense at the big-league level.
The full explanation comes from the "Allegory of the Window," which is here.
For pitchers, it is the reverse: if the pitcher can hold hitters such that they need to be "very fortunate" in terms of singles fallling in, then the pitcher scores well.
I consider this to measure a pitcher's "stuff" -- but with no preconceived notions. It is simply a measure of the pitcher's ability to get outs and limit damage (in terms of limiting walks and extra-base hits). I don't care if it's 98 or 78, groundballs or flyballs, it's just a measure of getting outs and limiting damage.
Once I realized I was producing a blizzard of numbers that weren't very intuitive, I converted everything to a 100 scale akin to OPS+, wherein the two component numbers combine to form the third in the same manner that OBP+ and SLG+ can be combined to get OPS+.
The resulting index for "Hitter's +/-" I have dubbed "Plate Skills Index" for hitters and, when recalculated for pitchers, "Command/Control Index."
The resulting index for "Plausibility" I have dubbed "Production Index" for hitters and "Stuff Index" for pitchers.
The first two can be combined to get the "Composite Index" for both types of players.
The full post on "What the Three Numbers Mean" is here.
Again, it's just my way of measuring, and presented here for info-tainment purposes. I have found, however, that players who go on to long-term MLB success have a near-100% record of scoring over 100 in the minors at least once before age 23.