Even those of us who have occasionally scoffed at run differential as a predictor of success will have to admit that 2015 was a big season for that statistic.
The scoffing hit a peak -- unofficially of course -- in 2007, when the D-backs finished with a -20 run differential. This should have put them below .500. And yet they somehow managed to win 90 games and the National League West, not to mention a subsequent NL Division Series.
Last season, however, was much more of what the run-differential purists had in mind. The top eight teams in run differential all qualified for the postseason, although not exactly in the order run differential would have predicted.
What does run differential say about the 2016 season? The sample size is small, of course, but the simple answer to that question can be summed up in two words: The Cubs.

But we'll get back to that in a moment. First, a review of the regular-season run-differential winners from 2015:
1. Blue Jays: +221
Toronto won the American League East, returned to the postseason for the first time in 22 years and advanced to the AL Championship Series. The Blue Jays had the best offense in the Majors with 891 runs.
2. Cardinals: +122
The Cards had baseball's best record with 100 victories, and they won the NL Central. St. Louis specialized in run prevention, posting the best team ERA in the Majors at 2.94.
3. Astros: +111
It was a breakthrough season for the Astros, as they emerged from rebuilding to win an AL Wild Card berth. They followed with a victory in the AL Wild Card Game, and then subsequently took the Royals -- who would go on to win the World Series -- to five games in the AL Division Series.
4. Pirates: +101
Pittsburgh's 98 victories gave it the second-best record in the Majors, as it qualified for the postseason for the third straight year. The Bucs had the second-best team ERA in the Majors.
5. Royals: +83
Kansas City had the best record in the AL, and it won the AL Central title. The Royals then topped their 2014 World Series appearance with a Fall Classic triumph. They have specialized in defying statistical analysis, but they're on more conventional ground here.
6. Cubs: +81
Chicago had the third-best record in the Majors with 97 victories. That was only good for third place in the NL Central, but the Cubs defeated the Pirates in the NL Wild Card Game. They then beat the Cardinals in the NLDS before falling to the Mets in the NLCS. The North Siders had the third-best team ERA in the NL. Team ERA was, in fact, a perfect predictor of the top three records in baseball.
7. Dodgers: +72
The Dodgers won their third straight NL West title, but they were eliminated by the Mets in the NLDS. Los Angeles had the fifth-best team ERA in the game.
8. Mets: +70
New York won the NL East, and it soared through the postseason to the World Series on the strength of dominant pitching. The Mets were fourth in team ERA in the Majors.
In a perfect run-differential world, the 10 postseason teams would have been in the top 10 in run differential. Not quite. Two teams that did not qualify took the next two places in 2015: The Giants were ninth at +69; and the Nationals were 10th at +68.
The other two teams that qualified for the postseason were:
11. Yankees: +66
The Yanks were the No. 1 AL Wild Card team, but they lost to the Astros in the AL Wild Card Game.
14. Rangers: +18
Texas won 88 games and the AL West with a marginal run differential. Not quite the 2007 D-backs, but still a commendable season.
This year, the Cubs have taken a commanding lead, with a run differential of +69 after just 20 games. They may not be able to keep up this pace, which would be +558 at the season's end. The Cubs do have baseball's best record at 15-5. The Cardinals are a distant second in run differential at a robust +41. That is better than their current 11-9 record would indicate.

Some people still aren't buying into run differential.
"It starts at zero, so it's biased in favor of offense," one NL executive said. "Look at last year. You can say the Blue Jays had the best offense, but you can't say that they were the best team."
In 2015, there is no question that run differential had value as a predictor of success. We acknowledge that and move on knowing that one perfect mechanism for measuring team achievement still remains: Check the standings.