By Andrew Mooney, Boston.com Correspondent

Following a 9-0 demolition of the Calgary Flames on Jan. 5, the Bruins stood in sole possession of second place in the Eastern Conference, one point behind the first-place New York Rangers. They looked like contenders to repeat as Stanley Cup champs. I didn’t think they could be — but then the bottom fell out. Since that game in early January, the Bruins have gone 18-18-2, dropping them to fourth in the conference with 91 points. What caused this sudden dropoff? An investigation of the Bruins’ erratic offensive output may provide the answer.

During their floundering start to the year—which I’ll define as the 3-7-0 month of October—the Bruins’ raw shot totals were not markedly different from their numbers the rest of the season; they averaged 33.4 shots a game over this period, as compared to 33.0 for the entire year.

Then came the torrid months of November and December, in which the Bruins raced back into first place in the Northeast Division behind a 21-3-1 record. They dominated on both ends of the ice, averaging 3.96 goals per game (scoring 5 or more goals 11 times) while allowing a mere 1.68 goals against. The rest of the NHL was on notice: play Boston, and prepare to get steamrolled.

We’ve seen what’s unfolded the last two months, during which the sputtering Bruins have a sub-.500 record. As of their March 19 victory over Toronto, their scoring average had dropped to 2.66 goals per game, and their opponents had outscored them by almost a half-goal per game (3.09 goals against)—a far cry from their previously dominant play.

However, the Bruins’ earlier success may have been distorted by their high even-strength shooting percentage, with which their fluctuating fortunes have trended closely. Their shot totals during November and December had not noticeably changed from their early-season slump; in fact, they had even dropped slightly, to 32.2 per game. Yet the Bruins’-even strength shooting percentage had risen all the way to 12.1 percent, up from 5.8 percent in October. For a bit of perspective, the team with the highest even-strength shooting percentage in 2010-11 was the Philadelphia Flyers, at 9.2 percent, and the league average typically hovers around 8.0 percent.

Interestingly, the Bruins’ shooting percentages have varied inversely with those of their opponents in each of these three time periods—in other words, as the Bruins struggled to find the net, their opponents did so comparatively easily, and vice versa. In October, Boston opponents shot a respectable 8.4 percent; in November and December, they shot just 5.1 percent; and in the present slide, 10.8 percent.

So what does this mean? One might think the Bruins were simply playing worse hockey, and maybe they were. During their rough patches, they may not have been getting the same quality shots with which they routinely racked up 5- and 6-goal games during their winning streak.

But that’s not the whole story; the change could just be the result of luck. The work of various hockey researchers has suggested that it’s much easier for teams to control the shot total of their opponents than the quality of those shots — that is, in aggregate, most shots on goal are indistinguishable in value. Since the shot totals of the Bruins and their opponents have been largely stable throughout the season, the hot and cold goal-scoring stretches can be attributed to random variation. The Bruins were due for a regression to the mean after November and December, and sure enough, they cooled off to start 2012.

I was first tipped off to this trend by an article from Grantland’s Katie Baker, who referenced the work of NHL blogger Cam Charron. Charron’s piece sums things up nicely.

Since … 2008, when a small Canadian website began recording NHL.com play-by-play data, only two teams, the 2009 Pittsburgh Penguins and the 2010 Washington Capitals, have finished with shooting percentages of higher than 10 percent. Boston’s 9.8 percent shooting rate by the time they hit the White House break wasn’t just due to come down: it already was dropping.

With four wins in their last five games, the Bruins appear to have righted the ship, at least for now. Their even-strength shooting percentage for the season has returned to a reasonable 8.7 percent. And as the cream of the Eastern Conference is concentrated in the Atlantic Division (New York, Pittsburgh, and Philadelphia), the Bruins are currently in line for a No. 2 seed in the playoffs. Still, given the improvement in the conference this year, they may need more of that shooting magic if they’re to make another deep run this playoff season.

As the old saying goes, you’d rather be lucky than good.

By Andrew Mooney, Boston.com Correspondent

The Bruins could be excused for nursing a hangover following their Stanley Cup victory in June – a $150,000 bar tab would leave anyone feeling a little under the weather. But it’s getting high time to climb out of bed and take a cold shower. It’s November, boys.

Or maybe there’s something more sinister at work: are the Bruins suffering the aftereffects of the dreaded “Stanley Cup Hangover”? As the theory goes, teams that compete into the summer have difficulty returning from the physical strain and emotional exertion of fighting for a championship. This carries over into the following season, a burden ultimately keeping them out of contention for a repeat championship.

There’s plenty of anecdotal evidence suggesting the reality of the Stanley Cup Hangover phenomenon. After hoisting the Cup in 2010, the Chicago Blackhawks floundered through much of 2011, squeaking into the playoffs as an 8th seed before their elimination in seven games by the Canucks. The NHL hasn’t had a repeat champion since the 1998 Red Wings. The two finalists from last year, the Bruins and the Canucks, haven’t met expectations during the current young season.

Do the numbers tell a similar story? Below are charts detailing the results for both Stanley Cup winners and losers since 1995, when the NHL settled on an 82-game schedule.

Over this period, Cup-winning teams suffered a dropoff of, on average, 6.67 points during the regular season, a difference amounting to between two and three seeds in the playoffs. Cup-losing teams experience a similar downturn, falling short of their results the previous year by about 7.5 points. This alone could account for a large part of the difficulty of returning to the finals: a lower seed in the postseason creates matchups against stronger teams and a lower likelihood of advancing in each round.

One interesting point to note is the high variance of results for teams that lost in the finals; their performance the following year tended to be drastically different from that of the previous year, for better or for worse. A near miss at the Stanley Cup could either be a motivating springboard to future success or a spirit-crushing defeat – something for Vancouver to keep in mind, given the Canucks’ current struggles.

It might also be that a team’s roster turnover from year to year has a lot to do with the severity of their “hangover.” Teams that stay mostly intact following a Stanley Cup victory might have an easier time bouncing back the following season. The ’10-’11 Blackhawks, gutted by free agency, would certainly bear this out; some of their struggles could be attributed to the fact that they returned a mere 55 percent of their minutes from 2010 to 2011. The Bruins, conversely, lost only three players in the offseason: Tomas Kaberle, Mark Recchi, and Michael Ryder.

However, a quick linear regression of the percentage of ice time a team returns against those teams’ changes in points from their Cup-winning year to the season after proved statistically inconclusive. In the model, only 20 percent of the variation in points could be explained by their roster turnover, in part due to the limited data. The NHL has only compiled individual player minutes since 1999.

Whether it’s appropriate to term these declines as “hangovers” is another question. A stellar regular season is a remarkable achievement in itself; making it to the Stanley Cup Finals is another thing entirely. It takes the convergence of many favorable circumstances to put together a run like the Bruins did – sufficient health, lights-out goaltending, and three Game 7 victories in one playoff season are not things you can bank on every year.

The reality may be that such success is not sustainable over a period of multiple seasons unless a team is approaching the level of dynasty, like the Red Wings in the mid- to late-‘90s, formidable on both ends of the ice. I doubt any realistic fan would put the Bruins in this category. Though they boast the league’s best goaltender in Tim Thomas, the offensive weapons in front of him, while serviceable, cannot be considered dominant. Certainly, young forwards Tyler Seguin, Brad Marchand, and Milan Lucic have the potential to get there in time, but at ages 20, 23, and 23 respectively, they can’t be counted on yet to carry an elite offense.

In short, Bruins fans could be in for a long, frustrating season. At 4-7-0, the Bruins have exhibited all the symptoms of the Stanley Cup Hangover, showing just how difficult it is to meet fans’ expectations after finally reaching the mountaintop. While there’s still plenty of hockey left to play, this doesn’t look like the sort of team cut out for a repeat. So cherish the Cup while you can. It may not be around much longer.