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NBA Playoffs history lesson -- What are the odds?

The Clippers 2-0 lead over the Grizzlies in their NBA Playoff series puts the Clippers in an advantageous position. Very advantageous, according to NBA playoff history.


The Los Angeles Clippers hold a 2-0 lead in the best of seven first round series against the Memphis Grizzlies. That's obviously good news for the Clippers and greatly increases their odds of winning the series. But by the same token, the Grizzlies will certainly point out that all the Clippers have done so far is hold serve, that Memphis only has to steal one game in STAPLES Center to win the series, that they could have two more chances to do just that. It all begs the question, just how likely are the Clippers to win this thing at this point?

From a purely probabilistic standpoint, the website sets the odds of the Clippers advancing to the second round given their 2-0 lead at 81%. According to the site, "all future unplayed games are assumed won/lost with a probability based upon relative team strengths." In other words, based on factors like won/loss record, margin of victory and the like, the site is doing a pure probability calculation that the Grizzlies will win four straight or four out of five against the Clippers. That probability turns out to be 19%, leaving the Clippers with an 81% likelihood of advancing.

Pretty good right? But what does NBA history tell us about this situation?

It turns out that NBA history tells us that these probabilities are too conservative. According to the encyclopedic website, which tracks the results of seven game series across every major sport in every conceivable situation, teams leading 2-0 in a seven game series have a .890 winning percentage across all sports (573-71). The winning percentage is even higher in the NBA, where teams up 2-0 have won 233 times, losing just 15 times. This .940 winning percentage is identical for all rounds of the playoffs and for the first round, where teams up 2-0 have gone 47-3.

Surely though you say, the record is not so one-sided when both of the wins occurred at home. After all, we always here that a series doesn't really start until the home team loses, and all the Clippers have done so far is win their home games. As it happens, the results are even MORE lopsided when the first two games are home wins. Teams in the Clippers' situation, up 2-0 after two home games, have a 201-12 (.944) record in all NBA playoff series and a 46-2 record in the first round (.958). While this may seem counter-intuitive at first, bear in mind that the team that hosts the first two games is by definition the team with the better record (or at least the team that won a tie-breaker) so there are factors dictating their victory in the series that go beyond the mere fact that they lead 2-0. The Clippers-Grizzlies series -- pitting two teams with identical regular season records against each other -- is somewhat unique, so clearly the Grizzlies' odds will be better than the general data set. For instance, Miami's 2-0 lead over Milwaukee is a very different situation than L.A.'s 2-0 lead over Memphis.

Continuing the history lesson, let's go back to 2006, to the only other time the Clippers had home court advantage in the NBA Playoffs. That season, the Clippers opened with two victories in STAPLES Center over the Denver Nuggets. In both the 2006 series and this year, the Clippers opening victories included a two point win and a double digit win. In an even stranger coincidence, the opponent scored the same number of points in both games of the two series (Denver lost 89-87, 98-87 while Memphis lost 112-91, 93-91). In 2006 the Nuggets managed to win Game 3 but the Clippers won the next two to close the series out in five games.

Speaking of Game 3, although NBA history overwhelming favors the team up 2-0 in the series, Game 3 is usually won by the home team. In NBA history, the visiting team is 229-273 (.456) despite being up 2-0 in the series.

And what does say about the Clippers odds going forward? Well, the site gives the Clippers a 33% chance of advancing to the Western Conference Finals, a 16% chance of winning the conference and advancing to the NBA Finals, and a 6% chance of winning it all. Bear in mind that these odds are cumulative. The probability of getting heads when you flip is coin is 50% -- the probability of getting heads twice in a row is 25%. But the probability of getting heads a second time after getting heads the first time is still 50%. Which means that the 33% chance the Clippers have of advancing to the Conference Finals takes into consideration the 19% chance that they won't get out of the first round. A little reverse engineering of these probabilities shows that the Clippers actually have a 41% chance of winning in the second round, a 49% chance of winning in the conference finals and a 38% chance of winning in the Finals -- assuming they advance to those rounds. I'll take that.