Before each round of the NHL Playoffs, Scott Cullen crunches a few numbers and comes up with an expected goals for and against for each team, based on shot differentials and save percentages to this point in the season.
In the first round, the team with the higher expected goals, using these calculations, won seven of the eight series, with the Los Angeles Kings' win over the St. Louis Blues upsetting the bid for perfection.
Round Two brought middle of the road results, 2-2, with Jonathan Quick leading the L.A. Kings to exceed expectations and the Pittsburgh Penguins tearing through Ottawa's top-ranked goaltending.
The Conference Finals played true to form, however, with Boston and Chicago both winning and, while it might have been a surprise at how easily they advanced, both were clear favourites by these calculations.
Since I'm the first one to emphasize that overall statistics (or standings) are not necessarily representative of the current value for a team, especially with respect to injuries, these statistics merely provide a baseline for the series, perhaps providing an idea what a team needs to do in order to emerge victorious.
In some cases, teams will simply need to keep doing what they've been doing throughout the regular season; in others, they might need better goaltending, or fewer shots against, or more shots for -- just something -- to provide better expected results in a seven-game series.
The calculations below are simple and the expected goals for each team in the series are determined by taking each team's shots for and against over the course of the season and splitting the difference.
So, Chicago has 31.4 shots on goal per game through the regular season and three rounds of the playoffs and Boston has allowed 29.7 shots on goal per game; the average of those two numbers is 30.6 shots, so that's the number that is then multiplied by (1 - the opposing goaltenders' save percentage) to determine an expected goals per game.
Finally, the number is multiplied by seven to indicate an expected goal total for a seven-game series. There's no guarantee that scoring more goals in a series will result in winning four games first, but the odds certainly favour the team that scores more.
Verdict: This is an even matchup, with a slight edge going to Boston because of Rask. It's not that Crawford hasn't played well for Chicago -- he obviously has -- but Rask's .943 save percentage in the postseason trumps Crawford's .935 and Rask also held an advantage in the regular season (.929 to .926) so there is some reason to believe that Rask may turn aside a few more shots.
If the difference is about five goals per 1000 shots and a seven-game series might yield approximately 200 shots, then the goaltending difference is only going to be worth about a goal. By no means is that decisive, rather it's reason for a slightly more favourable forecast. (Worth noting that the Blackhawks are -140 to -150 favourites to win the series, depending on the site.)
While we're looking at percentages, it's also worth considering that, in a short series, players may exceed (or fail to meet) their established performance levels. Blackhawks LW Bryan Bickell has been one of the exceptional ones, scoring on 22.9% of his shots in the playoffs, while Bruins RW Nathan Horton (22.9%) and C David Krejci (21.6%) are both over 20% as well. Eventually, regression catches up to that kind of shooting, but it could still hang on through one more series; such is the magic of small sample size.
On the other end of the spectrum, Blackhawks C Jonathan Toews has one goal on 51 shots (2.0%) and LW Brandon Saad has none on 35 shots, so they're due for better results. Bruins RW Jaromir Jagr is still seeking his first goal, despite 45 shots in the playoffs, and RW Tyler Seguin has one goal on 54 shots (1.9%), so those numbers wouldn't last over the long haul. If any of these players actually start scoring, that would figure to improve their respective teams' odds of success.
These are two of the top four possession teams, in both regular season and playoffs, so it's not like either one relies on their goaltender or special teams to an unreasonable degree. While neither team has been great on the power play in the playoffs (15.6% for Boston, 13.7% for Chicago) the Blackhawks have had the league's best penalty killing in the playoffs (94.8%), while Boston's 86.5% has been strong, just not the best.