Variable Team Strength Ratings

At the beginning of the season when previewing teams I introduced something I titled "V-SRS," which was a tweak of basketball-reference's team rating metric, SRS, that adjusted a team's SRS based on how strong their opponent was. Basically, it tests the idea that some teams run up the score on weak teams or others are stronger versus the best teams in the league. With the playoffs coming, I thought this was the perfect time to try for an entire set of rankings based on "V-strength."

Quick description: the team rating (point diff.) column is just a basic team strength metric adjusted for the schedule, including back-to-back games. It's very similar to SRS. Strength variance is the degree to which a team's strength rating varies based on how good the opponent is. I've provided two columns to illustrate this: a team's rating versus a +3 team, which is a typical playoff team and one near 50 wins, and what a team's rating would be versus a +6 team, which is a strong contender as most title-winners are near +6 or over. Since the metric needs to be tested over multiple years still, I sorted teams by their strength versus +3 teams because it's a more conservative estimate of how good they are against competitive playoff teams.

Team	Team rating (point diff.)	Strength variance	Team rating versus +3 team	Team rating versus +6 team
Los Angeles Clippers	7.27	0.15	7.90	8.53
Oklahoma City Thunder	6.60	0.31	7.68	8.76
San Antonio Spurs	8.01	-0.44	6.87	5.72
Houston Rockets	5.08	-0.02	5.20	5.31
Golden State Warriors	5.11	-0.17	4.78	4.45
Portland Trail Blazers	4.37	-0.24	3.83	3.28
Miami Heat	4.14	-0.18	3.77	3.41
Dallas Mavericks	2.93	0.13	3.49	4.05
Indiana Pacers	3.66	-0.15	3.37	3.09
Phoenix Suns	3.05	-0.04	3.11	3.16
Toronto Raptors	2.53	0.09	2.95	3.37
Minnesota Timberwolves	3.03	-0.19	2.62	2.21
Memphis Grizzlies	2.15	-0.09	2.05	1.95
Chicago Bulls	1.13	0.08	1.53	1.92
New York Knicks	-1.37	0.47	0.22	1.81
Washington Wizards	0.49	-0.45	-0.70	-1.88
Brooklyn Nets	-1.57	0.09	-1.13	-0.70
Atlanta Hawks	-0.84	-0.31	-1.62	-2.40
Denver Nuggets	-1.43	-0.15	-1.71	-1.98
New Orleans Pelicans	-2.03	-0.05	-2.00	-1.97
Detroit Pistons	-4.11	0.57	-2.23	-0.36
Sacramento Kings	-2.09	-0.10	-2.23	-2.38
Charlotte Bobcats	-0.92	-0.63	-2.67	-4.41
Cleveland Cavaliers	-3.83	-0.10	-3.97	-4.12
Boston Celtics	-4.90	0.03	-4.66	-4.42
Orlando Magic	-5.86	0.24	-4.97	-4.08
Los Angeles Lakers	-5.30	-0.43	-6.43	-7.56
Utah Jazz	-6.23	-0.38	-7.20	-8.17
Milwaukee Bucks	-8.42	0.31	-7.34	-6.26
Philadelphia 76ers	-10.66	-0.37	-11.62	-12.57

*Note: a positive strength variance means your team's rating increases as the opponent gets better, and negative means your team rating's gets worse as the opponent gets better

When the media cite records of, say, the Spurs versus playoff teams, they're essentially doing a weak version of variable team strength. However, they do not adjust for schedule or the point differential of those games. Thus, the variable team strength metric, something I'm calling "V-strength" for now, more accurately reflects how good these teams are versus the top competition without completely disregarding all the other games and with an objective statistical adjustment. 

One point here is that, yes, the Spurs were better against weak teams, though they rested their top guys so heavily that once the starters play more minutes the effect could be washed out. Also, I believe people are sleeping on the Clippers. They appear to play well against top competition, they're healthy at the right time, and they're being underrated because they're a new team on the big stage. The Mavericks and Bulls are two I would have thought of before crunching the numbers, as Dirk plays well in all situations and the Bulls have a top-notch defense and coaching to grind out wins versus better teams. The Heat, however, look worse, but perhaps with more playing time for Wade they'll punch at a higher weight class than their numbers indicate.

It's a new, untested metric, but it's good to quantify a natural question that's constantly arising -- how good are you against the best teams?