How do you judge the success of an NBA offense?
Just looking at points scored isn't enough, because that doesn't allow offensive efficiency to factor into the equation. For that reason, offensive rating—a pace-neutral metric that shows how many points a team scores per 100 possessions—is much better to look at.
But when attempting to rank teams historically, as we're doing here, that's still not good enough. After all, not every team with identical offensive ratings is made equal.
If two teams score 110 points per 100 possessions, which is better—Team A, which did so during a year in which defenses thrived, or Team B, which did so when everyone was scoring at a high level?
Team A should be the obvious answer, because context matters. And that's why ORtng+, or adjusted offensive rating, is the best inter-era metric for comparing offensive performances.
Calculating it isn't particularly difficult; just divide the team's offensive rating by the league-average offensive rating from the year in question, then multiply the result by 100. If a team scores 10 percent more than the average squad that year, it'll have a 110 ORtng+. If it scores 10 percent less, it'll have a 90 ORtng+.
A score of 100 means the offense was perfectly average, a feat most recently achieved by the 2012-13 Dallas Mavericks and Toronto Raptors.
When determining the 20 best point-scoring machines in NBA history, flashiness doesn't matter. Neither does points per game. Nor does memorability, subjectivity or the team's win-loss records.
ORtng+ is all that comes into play. Analyses like this have been run before, notably by Hardwood Paroxysm's Andrew Lynch and Ian Levy, but this is taking it to a whole new level by running things pre- and post-merger.
Note: All stats, unless otherwise indicated, come from Basketball-Reference.com.