Monday, January 19, 2009

My Rating System, and why it is the way it is.

Josh from the Excellent Big Ten Geeks blog asked me about my rating system formula, and I thought I'd write up a full explanation.

The non-secret Formula:
Points + Rebounds + Offensive Rebounds + [2 x(Steals+Blocks)] + (2.5 x Assists) - [Missed FGs + (2 x Turnovers) + (Missed FTs/2)]

Divide by game for per-game rating (hpg), and divide by individual possession for per-possession rating (hpps).

Explanation/non-defense thereof:
I started working the formula up back when I was following the NBA in the early '90's, sort of as a way to figure out who might be best in on Fantasy NBA teams. A columnist at USA Today, maybe, proposed some model for comparing players, and I kind of went with it from there. I didn't think of applying it to the college game until a few years ago, when I came across the Big Ten Wonk. He had so many things covered in tempo-free ways, it was inspiring but also intimidating. Effective field goal % and rebounding rates and so much more, as you all well know. However, I like things in a tidier package for comparison's sakes, tho. Kyle Whelliston at Basketball State has a comparable model, but it's pretty much a straight addition of the box score.

Here's the basics: I wanted to reward not only the ability to score points efficiently, but also the other aspects of the game that are so important but not as hyped. And with the Big Ten Wonk's focus on tempo-free comparison, I realized that the possession was the important thing I wanted to factor in. I remember Bob Knight saying about freshmen, that they didn't understand that when they turned it over, that was two points the team lost. And in general, in per-possession stats, that's true: most teams average around 1 point per possession on offense and give up close to the same on defense. But guys like Scottie Pippen, Ekpe Udoh, and Jamarcus Ellis never seemed to get the credit they deserved because their per-game scoring wasn't near other players while their rebounding, passing (well, not Udoh), and ability to get defensive stops went unrecognized. I thought a formula like this might help even it out.

So, obviously points were points, and steals were plus two points, and turnovers were minus two. Offensive rebounds secure a possession where a team shouldn't have one, so that's plus another two points. Blocks are little more difficult, because they aren't always a sure stop, but I figured someone who block shots probably also intimidates or changes shots enough to balance that out: plus two for them as well.
I especially wanted to reward assists. I grew up in Southern Indiana, so passing was always a premium, but it's always irritated me that assists are valued so lightly in other computations (the NBA and Whelliston are examples, but just about every sport puts assists as one point). Especially in basketball, where assists can be on three-point plays or shots, or what should be an assist can so easily turn into a foul on the other team and two more points, to boot. But I figured with a rough count that 30+% of all points come from free-throws and the additional point from three-point makes, so I rounded up to 2.5 points per assist. Really, it should be 2.3 or less, but I was using missed free-throws as minus half-a-point, so for ease, I figured it balanced out. Also, since it's been revealed that the home games result in higher assist counts for the home team, my system could be criticized for putting a premium on the most subjective measure in the box score. But, over 16+ conference games evenly split between home & road, I hope it balances out, too.

I count missed shots as minus one point because offensive rebounds do happen, and some teams used the missed shot as a feature of their offense (Michigan State under Izzo, as well as the Fab Five). And I count rebounds as only one point, as I felt that defensive rebounds are something that basically should happen. Someone else from your team will likely grab that board if you don't. And that's perhaps unfair. But I saw a lot at both the college and professional level of big men grabbing rebounds when noone was near them and snarling or screaming. Besides the aesthetically unpleasantness, I just didn't think that say, DJ White should get as much credit for a rebound on the defensive board -which was often snagged over a teammate (namely Ellis), - as opposed to the rarer and I think harder task of getting a offensive rebound. But, at the end of the season, I may try a tweaked version where I count Def. rebounds as plus two points and missed shots as minus two points. I could also count missed free-throws as minus a full point, also.

The one thing I'd like to do, but sort of flies against the intent of my system, is to reward three-point makes with an extra point due to their value to any offense. It's hard to operate an offense if you don't have shooters to keep the defense from packing it in. But it would require valuing threes as more than just three points in the system, but really as four points each. But it might be necessary in recognizing the value that a guy like Jason Bohannon has to his offense, and especially if I start counting defensive rebounds as two points.

Any (collegial) thoughts or suggestions are, as always, completely welcome.

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