## 2999RE: [APBR_analysis] Re: Team Ratings (adjusted for schedule strength)

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• Jan 6, 2004
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Thanks, clearly my figure of 2/3 home wins was based on 1970s-1980s
memories, in recent years the figure's been more like 3/5.

There's a lot of little detailed questions to be answered, such as
which Home Win% figure to use, let's just pick this year's current
value of 62%.

Using ssims' ORate and DRate numbers, that corresponds to a team
having approximately a 3.5 point advantage, in terms of ORate -
DRate difference.

So if a team has played 12 home games and 8 away games, it's got
a 4-game imbalance, worth a cumulative 4*3.5 point ORate-DRate
difference = 14, which spread over its 20 games is 0.7 points
of ORate-DRate differential.

So if the initial rating has the team appearing to be a .500
team with ORate = 100 and DRate = 100, an estimate which
corrects for its excessive home games would be ORate = 99.3
(or, the .7 points could be split evenly between ORate and DRate).

This is a crude measure of course;, if we had home-road splits
of O and D, we could do separate corrections for ORate and DRate.

And for theoretical correctness we should apply the same Home-
Road correction to the Opponent's ratings, as well as the
Opponents' Opponents' ratings.

Better still would be to apply the correction to individual
game scores, rather than each team's aggregate totals; and
to base the ratings on the outcomes of the individual games
rather than the aggregate season totals; and to permit
individual teams to have differing home bonuses instead of
assigning all teams a 3.5 home bonus; and to solve the
simultaneous equations for looking at opponents'
opponents' opponents' ... ad infinitum; and etc. etc.

But those procedures would require a lot more data and a lot
more work. This crude home-road correction is simple and
I would guess cleans up a good chunk of the home-road bias.

--MKT

-----Original Message-----
From: Dean LaVernge [mailto:deanlav@...]
Sent: Monday, January 05, 2004 8:24 PM
To: APBR_analysis@yahoogroups.com
Subject: RE: [APBR_analysis] Re: Team Ratings (adjusted for schedule
strength)

On 5 Jan 2004 at 9:43, Michael Tamada wrote:

>
> I was thinking of a simpler, cruder home-away correction. Although
> some teams seem to thrive at home and wilt away from it (Utah) and
> others seem to be road warriors as good on the road as at home (Boston,
> Seattle), I was thinking in terms of simply giving a single universal
> home-away correction that would be applied to every home team's offense
> rating or defense rating (or both, but I think this wouldn't really matter,
> because it'd simply be a constant to be added or subtracted).
>
> We would still need some home-away split data, but even if that's
> unavailable we could estimate what the home bonus should be: in
> most years, NBA teams win about 2/3 of their home games (I haven't
> looked at this year's data). Comparing a .667 team to a .500 team,
> how much better would its offense have to be to move it from .500
> to .667? (Or equivalently, how much better would its defense have
> to be?) Whatever that figure is, that's the home bonus to give
> to the home team's offensive rating (or defensive rating).
>
> Crude but simple and I think it would significantly help correct
> for teams which have had schedules which were either (a) unbalanced
> with respect to home and away games or (b) balanced with respect
> to home and away, but unbalanced in terms of having tough or easy
> road opponents, and vice-versa at home.
>
>
> --MKT
>

Here is the Home/Away records for the NBA (2004 Season through games of 1/4/2004)

Season Wins Losses % Wins Losses %
1947 202 129 0.610 129 202 0.390
1948 107 85 0.557 85 107 0.443
1949 212 132 0.616 132 212 0.384
1950 351 167 0.678 167 351 0.322
1951 254 85 0.749 85 254 0.251
1952 213 80 0.727 80 213 0.273
1953 195 83 0.701 83 195 0.299
1954 151 84 0.643 84 151 0.357
1955 139 59 0.702 59 139 0.298
1956 141 80 0.638 80 141 0.362
1957 172 76 0.694 76 172 0.306
1958 150 85 0.638 85 150 0.362
1959 148 80 0.649 80 148 0.351
1960 149 84 0.639 84 149 0.361
1961 156 85 0.647 85 156 0.353
1962 166 107 0.608 107 166 0.392
1963 184 109 0.628 109 184 0.372
1964 185 126 0.595 126 185 0.405
1965 178 125 0.587 125 178 0.413
1966 197 89 0.689 89 197 0.311
1967 193 128 0.601 128 193 0.399
1968 241 182 0.570 182 241 0.430
1969 315 206 0.605 206 315 0.395
1970 312 207 0.601 207 313 0.398
1971 402 262 0.605 262 402 0.395
1972 385 277 0.582 277 385 0.418
1973 393 268 0.595 268 393 0.405
1974 410 262 0.610 262 410 0.390
1975 472 266 0.640 266 472 0.360
1976 484 254 0.656 354 484 0.422
1977 634 268 0.703 293 609 0.325
1978 610 292 0.676 292 610 0.324
1979 600 302 0.665 302 600 0.335
1980 588 314 0.652 314 588 0.348
1981 586 357 0.621 357 586 0.379
1982 565 378 0.599 378 565 0.401
1983 585 358 0.620 358 585 0.380
1984 640 303 0.679 303 640 0.321
1985 601 342 0.637 342 601 0.363
1986 617 326 0.654 326 617 0.346
1987 627 316 0.665 316 627 0.335
1988 640 303 0.679 303 640 0.321
1989 694 331 0.677 331 694 0.323
1990 713 394 0.644 394 713 0.356
1991 730 377 0.659 377 730 0.341
1992 689 408 0.628 408 699 0.369
1993 676 431 0.611 431 676 0.389
1994 677 430 0.612 430 677 0.388
1995 661 446 0.597 446 661 0.403
1996 718 471 0.604 471 718 0.396
1997 684 505 0.575 505 684 0.425
1998 708 481 0.595 481 708 0.405
1999 452 273 0.623 273 452 0.377
2000 726 463 0.611 452 737 0.380
2001 711 478 0.598 478 711 0.402
2002 703 486 0.591 480 709 0.404
2003 747 442 0.628 442 747 0.372
2004 297 179 0.624 179 297 0.376
NBA 25136 14716 0.631 14824 25139 0.371

DeanL