Three years ago, Daniel Sedin was the No. 1 scorer in the NHL, hoisting the Art Ross Trophy after a magisterial 2010-11 season. He also won the Ted Lindsay Award, as the most outstanding player, voted on by the league's players.

Today, the 33-year-old Vancouver Canucks forward is mired in the worst scoring slump – goalless in 19 consecutive NHL games – since his second year in the league, when he was 21. His shooting percentage – goals per shots taken – is his worst ever, at 6.8 per cent, and among the lowest in the league.

It didn't get better at the recent Sochi Winter Olympics, where his country, Sweden, reached the gold-medal game but was shut out by Canada 3-0. In six games for Sweden, Sedin registered 16 shots, scoring only once.

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What is wrong with Daniel Sedin is a question Canucks fans and hockey watchers have debated with increased urgency this season. Theories range from advancing age to the changing style of play in the NHL that favours more grinding goals rather than the skilled plays in which Sedin and his twin brother, Henrik, specialize.

But others note a striking demarcation point: The major concussion Sedin suffered two years ago (March 21, 2012), when Chicago Blackhawks defenceman Duncan Keith elbowed him in the head. Keith was suspended five games and Sedin, whose symptoms included dizziness, was out four weeks.

According to interviews with concussion experts, there is no way to prove a link between Sedin's brain injury and his drop in performancein the ensuing years.

Many players recover from concussions, their skills restored, and, in an interview, Sedin insisted he is fine and healthy. In fact, there is an absence of research on athletes' performance in the years after a concussion. Even with the spotlight on concussions in recent years, the injury – especially its nuances – remains poorly understood.

"It's a really good question," said Anthony Kontos, assistant director of research at the renowned concussion program at the University of Pittsburgh Medical Center. "Currently, we don't have longer-term research follow-ups where we look at athletes two and maybe three and four years down the road to see what if any lingering effects there are related to this injury."

There is no doubting Sedin's extraordinary fall, however, and a Globe and Mail data analysis illustrates the depth of the decline compared to other players.

The collapse of his shooting percentage is far greater than any other goal-scoring forward in the league of his age, and notably worse compared with other NHL scoring title winners or MVPs since 1980.

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The main analysis (download spreadsheet) looked at players' shooting percentage in the four years up through age 31 – when Sedin suffered his concussion – and the two years after. In the four seasons, including playoffs, up to his concussion, Sedin played 346 games and scored 149 goals on 1,178 shots – a 12.6-per-cent rate, the level of a top-end scorer. In the 113 games after the concussion, Sedin has 25 goals on 343 shots – a 7.3-per-cent rate.

The decline in scoring potency is 42.1 per cent, far greater than the 11 other forwards in the NHL considered in the data analysis – players who are the same age as Sedin and have scored at least five goals this season.

In fact, the median result of the 11 players is not a decline but a 5.5-per-cent improvement in shooting percentage, buoyed by the likes of Joel Ward of the Washington Capitals and his hot hand the last two seasons. The two players most similar to Sedin have seen modest declines: fellow Swede Henrik Zetterberg, whose shooting percentage has fallen 10 per cent; and Henrik Sedin, a pass-first centre whose percentage is down 7.1 per cent.

Analysis of 12 other players – from Wayne Gretzky to Jarome Iginla – who have either won a scoring title or MVP award since 1980 reveals similar results, using the same time spans.

Is Daniel Sedin's decline a result of his concussion? According to brain-injury experts, it is impossible to make a causal connection.

Recent research by Kontos indicates symptoms such as dizziness, which Sedin experienced, is a risk factor for prolonged recovery. Still, experts say if a brain properly heals after a concussion, an athlete should not be adversely affected afterward. Doctors in interviews did note each person experiences brain injuries differently and some seem to be more susceptible than others.

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"Concussions," Kontos said, "are individual, much like snowflakes are."

Scientific research on brain injuries has reached a new level of intensity in the past several years, spiralling out from the controversies in the NFL.

"It's hot and heavy in a number of centres to track down exactly what are the long-term effects and can we quantify those with an objective test," said Charles Tator, a neurosurgery professor at the University of Toronto and senior scientist with Toronto Western Hospital.

Tator and his colleagues have recently completed a study of more than 125 athletes who had postconcussion syndrome – which Sedin has not been diagnosed with – and the analysis is being reviewed for publication in a scientific journal. The syndrome can last years, and sometimes forever, Tator noted.

Many other star NHL players, such as Sidney Crosby and Jonathan Toews in recent years, have returned from concussions and played as well after as before. While Crosby and Toews are younger than Sedin, Crosby suffered a far-more difficult and lengthy recovery, during which his future in hockey was in jeopardy.

"The analysis [of Sedin] is pretty striking," said Chris Nowinski, co-director of Boston University's Center for the Study of Traumatic Encephalopathy, a nexus of work on concussions and their long-term impact on retired football players. "The most likely scenario is it's a natural drop off, but you'd never overlook a brain injury, just like you'd never overlook a knee injury."

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To Sedin, everything is fine – except the feel of his now-seemingly vanished scoring touch. He blames himself for being unable to convert scoring chances into goals.

"People keep asking about that incident, but I'm fine," Sedin said in an interview after a practice in late January. "I was fine playing in the playoffs that year, and it's been good. So it's not a problem. I feel totally fine."

Sedin is getting shots on net, and there is no discounting the simple matter of luck.

"I can only blame myself for missing the chances," he said. "I mean, I've had breakaways, empty nets. It's more about executing, more than anything. The chances are there. It's a matter of putting them in."

Sedin has had successful stretches since his concussion. In the first month of this season, last October, before he and his brother signed a four-year contract extension, Sedin had six goals in 15 games, scoring on 11.5 per cent of his 52 shots. The new contract is for $7-million (U.S.) per year, a raise from the $6.1-million per year, five-season deal the twins are finishing.

The Canucks return to post-Olympics action on Wednesday, at home against the St. Louis Blues, with fans hoping Daniel Sedin will return to form as Vancouver fights for a playoff spot.

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Team officials have pondered the concussion question as well.

"I don't like to make presumptions about any head injuries and lingering effects, short-term and long-term issues," Canucks general manager Mike Gillis said in late January, on sports radio in Vancouver. "We're really at the beginning of trying to understand how brain injuries occur and what the long-term results are."

Gillis pointed to last year's unusual lockout-shortened season, in which the Canucks were without Ryan Kesler for much of the campaign, which allowed opponents to focus more on the Sedins. Also, while Gillis did not note it, the Canucks' power play has fallen apart and ranks among the lowest in the league, in part because of Sedin's decline.

Gillis cited a broader change in the NHL's style of play, last season and this one, which he said has teams defending more aggressively, with more focus on shot blocking. The Canucks, he said, have been slow to adjust. Highlight-reel goals are rarer.

"That, more than anything," Gillis said, "has resulted in skill players not scoring skill goals a lot of the time."