Friday, December 20, 2013

Elite Soccer Players Run Less

Millions of pounds may be splashed on elite footballers in the English Premier League, but it is those who play in the second and third tier of football who run further on the pitch, new research reveals.

For years, players in the top tier of English football have been paid much higher wages compared to those in the Championship and League One. However, research at the University of Sunderland has found it is those in the lower leagues who are covering a greater distance at a higher intensity.

Research published in the journal Human Movement Science analysed 300 players in the English Premier League, Championship and League One. It is the first time research has looked at the match performance across all three divisions.

The research found that those in League One ran a lot further at a higher intensity than those in the Championship. The same was true when Championship players were compared to those in the Premier League. The researchers believe this could be due to more teams adopting a long ball style of play the further you go down the football pyramid.

However, academics did find that those playing in the Premier League performed a greater number of passes and successful passes. They also received the ball more often and had more touches of the ball than those in the Championship and League One.

The research, 'Match performance and physical capacity of players in the top three competitive standards of English professional soccer', could also back up the belief that players at a higher standard have a far higher level of technical skill, and do not use the long ball tactic of 'kick and rush'.

Additionally, the research found that when players were relegated from the Premier League to the Championship, they began to run more distance at a higher intensity. However, when players moved in the opposite direction they didn't change the levels of running and intensity.

Dr Paul Bradley, led the research and is a senior lecturer in Sport and Exercise Science at the University of Sunderland, said: "This research highlights that the long ball game does make you work harder, and that the context of the game dictates how each individual or team works. Some of the results were quite surprising as we expected there would be differences in the technical areas between the leagues, but not the physical nature."

The report stated: "The data provides new insight into the possible impact technical characteristics have on match running performances and highlights that players at lower standards could tax their physical capacity to a greater extent….These findings could be associated with technical characteristics inherent to lower standards that require players to tax their physical capacity to a greater extent."

Friday, November 29, 2013

What's the Sound of a Hundred Thousand Soccer Fans?

Mention vuvuzela to soccer fans, and they may cringe. The plastic horn rose to prominence during the 2010 World Cup in South Africa, where tens of thousands of those instruments blared in packed stadiums. The loud, buzzing noise soon became a major annoyance, disrupting players and even fans watching on TV.

Now, for the 2014 World Cup in Brazil, organizers have introduced the maraca-like caxirola as the official instrument of the event. The caxirola, based on the African caxixi, was invented by Brazilian musician Carlinhos Brown to be more subdued than the vuvuzela. To see if this was really the case, Talita Pozzer and Stephan Paul of the Federal University of Santa Maria in Brazil studied the acoustics of the instrument, finding that a single caxirola, at least, poses no threat to the user's ear.

Their work will be presented at the 166th meeting of the Acoustic Society of America, held Dec. 2-6, 2013, in San Francisco, Calif.

In their analysis, the researchers asked 22 volunteers who had never seen the instrument to play it as they thought it should be played, finding that people tend to either shake it along its longer axis or its shorter axis. A recording device placed at the ear of each subject measured the sound of the caxirola.

The researchers found that if shaken along the longer axis, the instrument produces twice the sound energy as when shaken along the shorter axis. But because volume depends logarithmically on the sound energy, the difference is only just noticeable to the ear. In both playing styles, the sound pressure levels were comparable to that of a normal conversation – and roughly 45 decibels lower than that of the vuvuzela, corresponding to 1/30,000th times the sound energy. In other words, you would need 30,000 caxirolas to produce the same sound pressure level as a single vuvuzela.

The researchers also captured the acoustic signature of the caxirola played in both styles, measuring how the frequency and intensity of the sound varies over time. The signature was similar in both cases.

The next step, Paul said, is to measure the caxirola's sound power levels, which, unlike sound pressure levels, are independent of distance and the instrument's surroundings. The researchers can then input those measurements into a computer model of soccer stadiums, simulating exactly what kind of noise thousands of caxirolas would make, showing whether or not it would be harmful.

Since its introduction last year, the caxirola has already been mired in controversy. After disgruntled fans hurled the instrument on the field during a match in April, officials banned the instrument for the Confederations Cup last summer. Whether the caxirola will be distributed during the 2014 World Cup has yet to be determined, Paul said.

Perhaps it's not the caxirola's acoustics that's a cause for concern – but its aerodynamics.

Thursday, October 10, 2013

Soccer (football) players suffer more injuries when their team is ahead

Male football players are at a greater risk of injury five minutes after a card has been given or after a goal has been scored. The frequency of player injuries also increases when their own team is in the lead. These are the findings of researchers at the Sahlgrenska Academy, who, in collaboration with Fifa, have analysed injuries over the last three World Cup tournaments.

Football players do not just injure themselves whenever and however. On the contrary, injury frequency follows a clear pattern that is dependent on how various events in the course of a match affect players’ emotional and physical states.

This is borne out by three new studies conducted at University of Gothenburg’s Sahlgrenska Academy with the support of the international football association, FIFA.

Greater risk for players in the lead

The studies, which are based on injury statistics from the 2002, 2006 and 2010 World Cup tournaments for men, and which were published in the British Journal of Sports Medicine, show that:

• Injury frequency varies depending on whether a team is winning, losing or if the outcome is not yet decided. Players in winning teams are at the greatest risk of injury.

“This may be due in part to the fact that a losing team starts to play more aggressively,” says Jaakko Ryynänen, a PhD student at the Sahlgrenska Academy who contributed to the study.

Exposed position for strikers

• The risk of injury varies between the various positions, the frequency of injury being greatest amongst strikers:

“One possible cause is that the results of any one match are very important in international tournaments. This may accentuate the role of the strikers, leading to increased pressure on them,” says Jaakko Ryynänen.

• There is a direct link between the number of free kicks and the number of injuries per match. A match with more free kicks has a higher injury frequency.

• Injury frequency increases within a five minute period after a yellow or red card is issued, and following injuries and goals.

“One theory is that players lose their concentration following disruptive breaks in play, which then increases the risk of injury,” says Jaakko Ryynänen.

Surprising finding

A surprising finding is that the number of injuries per World Cup match increases if there is a longer break between matches.

“It sounds contradictory that the risk of injury increases with longer recovery times, but our theory is that this may be due to players losing their focus on match games after a break of several days. Perhaps teams also play at a higher level of intensity after they have rested for a number of days and have more energy.”

Prevent injuries

According to Jaakko Ryynänen these studies are important in terms of being able to prevent injuries.

“Our primary goal is to contribute with knowledge that can prevent injuries. The ability to recognise periods of matches when the injury incidence is high may be important in terms of preventive measures, for example replacing players at risk of suffering a repeat of a previous injury. Since there are more than 260 million football players in the world, preventive measures could help a lot of people. “

Temporary red card

Continued research could also result in new rules. Jaakko Ryynänen mentions as one example the introduction of temporarily sending off players for aggressive behaviour, as is the case with ice hockey.

“This is something for the governing bodies of football to consider. For our part, we will continue our research in order to identify more opportunities for injury prevention, and to see whether the conclusions we draw are also applicable to football at lower levels. “

The article “Foul play is associated with injury incidence: An epidemiological study of three FIFA World Cups (2002-2010)” will be published in the British Journal of Sports Medicine on 15 October.

Link to the article

The article “Increased risk of injury following red and yellow cards, injuries and goals in FIFA World Cups” will be published in the British Journal of Sports Medicine on 15 October.

Link to the article

The article “The effect of changes in the score on injury incidence during three FIFA World Cups” will be published in the British Journal of Sports Medicine on 15 October.

Link to the article

Tuesday, August 13, 2013

Automated analysis finds weakness in soccer coaching strategy

Review of 380 games suggests away teams should be more aggressive

Investigators at Disney Research, Pittsburgh, are applying artificial intelligence to the analysis of professional soccer and, in one application of the automated technique, have discovered a strategic error often made by coaches of visiting teams.

The common wisdom that teams should "win at home and draw away" has encouraged coaches to play less aggressively when their teams are on the road, said Patrick Lucey, a Disney researcher who specializes in automatically measuring human behavior. Yet the computer analysis suggests that it is this defensive-oriented strategy, and not officiating, that reduces the likelihood of road wins.

The researchers from Disney Research were assisted by Dean Oliver, Director of production analytics at ESPN. The team presented its findings at the Conference on Knowledge Discovery and Data Mining (KDD 2013) in Chicago.

Though soccer was the focus of this study, the researchers say their techniques are applicable to other team sports that feature continuous play, including basketball, hockey and American football.

An analysis of all 380 games from a 20-team professional soccer league's 2010-2011 season found that performance measures such as shooting and passing percentage were similar for home and visiting teams.

"My intern, Joe Roth, first noticed this while digging into the passing patterns of different teams. He found that they had approximately the same passing and shooting percentages at home and away. But where they had possession was very different," Lucey said.

At home, the team had the ball in its opponents' defensive third more often – and thus had more shots on goal – than when on the road and played a more defensive, counterattacking style. It was a pattern the researchers discovered held true for nearly every team.

"Visiting coaches are setting their teams up for failure from the get go," Lucey said of the common strategy. "They're not opening themselves up for randomness. The fault doesn't lie with bad calls from the referees."

Though human experts may have a feel for the game that no computer could match, Lucey said computers also have advantages over humans. "An expert might have a gut feeling," he said, "but an expert wouldn't be able to remember all details of all 380 games."

Professional sports teams today increasingly use quantitative methods to analyze performance. Some sports, notably baseball, lend themselves to such analysis because games are naturally divided into plays and sets. Soccer, on the other hand, is continuous and low-scoring, which makes analysis difficult, even though data is plentiful.

Rather than track player positions, for which data is scarce, the Disney researchers used ball action data – time-coded information about everything that is happening to the ball. This information is typically used for online visualizations of matches and is manually compiled by Opta, a commercial sports data supplier.

For the 2010-2011 season, that amounted to 760,000 ball action notations. The Disney software uses this data to infer the position and possession of the ball for every second of 380 games. It then divides the field into different areas and then counts how many times the ball was in each area over a specified time.

This yields "entropy maps," which model the uncertainty of a team's behavior in different areas of the field. Teams with high entropy spread the ball around and are harder to predict; low entropy teams have players who tend to stay within certain areas of the field.

By combining these entropy maps with commonly used match statistics such as passes, shots on goal and fouls, the automated analysis can distinguish between teams with high accuracy, the researchers have found.

The analysis of road team strategy is just one application of this automated technique, Lucey said. It could become a tool for coaches to track their team's progress or to provide insights for developing game plans, as well as an aid to television commentators.

Tuesday, July 16, 2013

Baseball players enjoy successful long-term results after elbow surgery

Baseball players undergoing ulnar collateral ligament (UCL) surgery are able to return to the same or higher level of competition for an extended period of time, according to research presented today at the American Orthopaedic Society for Sports Medicine's (AOSSM) Annual Meeting in Chicago, IL.

"Previous studies showed successful return to play after UCL surgery, but we were also able to evaluate each athlete's career longevity and reason for retirement," commented lead author, Daryl C. Osbahr, MD of MedStar Union Memorial Hospital in Baltimore. "These players typically returned to play within a year of surgery and averaged an additional 3.6 years of playing time, a significant amount considering the extensive nature of this surgery in a highly competitive group of athletes. They also typically did not retire from baseball secondary to continued elbow problems."

The study examined 256 patients, including high school, college and professional baseball players, and were contacted an average of 12.6 years after their UCL reconstruction. Approximately 83 percent of these athletes were able to return to the same or higher level of competition, with only 3 percent reporting persistent elbow pain and only 5 percent noting limitation of elbow function during day-to-day activities.

"UCL injuries used to be considered career-ending," Osbahr noted. "Now players are consistently able to return to play at a high level while also enjoying excellent long-term outcomes."

While approximately 243 (95%) of the athletes studied had retired by the minimum 10-year follow-up, 238 (98%) still participated in throwing at a recreational level with most reporting no elbow pain.

The research earned AOSSM's O'Donoghue Sports Injury Research award, given annually to the best overall paper that deals with clinical-based or human in-vivo research.

Tuesday, July 9, 2013

In baseball, bigger still better

Max Scherzer leads Major League Baseball in wins. As a pitcher for the Detroit Tigers, he hasn't lost a game this season.

His 6-foot, 3-inch frame is a telling example of constructal-law theory, said Duke University engineer Adrian Bejan. The theory predicts that elite pitchers will continue to be taller and thus throw faster and seems also to apply to athletes who compete in golf, hockey and boxing.

Studying athletes -- since most sports are meticulous in keeping statistics -- provides an insight into the biological evolution of human design in nature, which Bejan terms the constructal-law theory.

Bejan has already demonstrated that runners and swimmers have gotten bigger and taller over the past century. Now he's applying his theories to other sports, including team sports. In those cases, forward momentum was a major factor in the athletes' successes.

What unites golf, baseball and hockey is the "falling forward" motion involved, whether it is a pitcher's arm or golfer's swing. Basically, the larger and taller the athlete, the more force he or she can bring to bear as his or her mass falls forward, Bejan said.

The results of his analyses were published online in the International Journal of Design & Nature and Ecodynamics.

"Our analysis shows that the constructal-law theory of sports evolution predicts and unites not only speed running and speed swimming, but also the sports where speed is needed for throwing a mass, ball or fist," Bejan said. "The sports of baseball, golf, hockey and boxing bring both the team and the individual sports under the predictive reach of the constructal theory of sports evolution."

The falling forward idea states that the larger and taller the individual, the more force can be applied as the ball is hurled forward. For example, former major leaguer Randy Johnson, a 6-foot, 10-inch pitcher, was a terror to batters during his career, notching two no-hitters, five Cy Young awards for best pitcher and the record for strikeouts by a lefthander.

"According to the constructal law predictions, the larger and taller machine, like medieval trebuchets, is capable of hurling a large mass farther and faster," Bejan said. "The other players on the baseball field do not have to throw a ball as fast, so they tend to be shorter than pitchers, but they too evolve toward more height over time. For pitchers, in particular, height means speed."

In golf, despite the advances in ball and club design, taller competitors have been driving the ball farther than shorter golfers. In 2010, Bejan found the average golfer in the top 10 of driving distance was on average 2.5 inches taller than the average golfer in the bottom 10 of driving distance.

"This shows that height plays a definite role in the success of an athlete in golf," Bejan said. "The increase in driving distance with body mass is due to the fact that larger moving bodies are capable of exerting greater forces. Also, the increased size of clubheads has had a distinct affect on the game. The average driving distance on the Professional Golfers Association (PGA) tour has risen 30 yards in the past 30 years."

The same reasoning also applies to sports equipment, such as golf clubs and hockey sticks. Just as golf clubs have become lighter and more flexible to increase speed of swing, and thus distance, so have hockey sticks, Bejan said.

In terms of boxing, Bejan notes similar trends, even though boxers are classified and compete in specific weight classes. While height and arm reach help boxers, they cannot be too tall, because then they lose core strength, which lessens the falling forward force that powers the punches.

"We looked at the 25 greatest fighters in the lightweight and welterweight classes and found that these boxers have been able to maximize punching power by gaining size without going over weight limits," Bejan said. "They have done this by adding muscle and cutting water weight before a fight, and these techniques over time provide an explanation for the improvement in boxers' size and knockout rates."

The work of Bejan's group was performed during the course "Constructal Theory and Design," developed at Duke with the support of the National Science Foundation. Other members of the team were Duke's Sylvie Lorente, James Royce, Dave Faurie, Tripp Parran, Michael Black and Brian Ash.

Tuesday, June 11, 2013

Soccer Headers Can Lead to Brain Injury

Advanced scans show that soccer players who head the ball frequently have changes in the white matter of their brain that mirror those seen in traumatic head injuries.

Additionally, the study published in the journal Radiology revealed that these athletes face a higher risk of developing memory and thinking problems.

The current study follows a previous one conducted by the same researchers that found that frequently heading the ball during soccer games can lead to brain injury. They noted that all five areas of the brain were affected.

Michael L. Lipton, M.D., Ph.D., associate director of Einstein's Gruss Magnetic Resonance Research Center and medical director of MRI services at Montefiore, the University Hospital and academic medical center for Einstein explained:

"We studied soccer players because soccer is the world's most popular sport. Soccer is widely played by people of all ages and there is concern that heading the ball - a key component of the sport - might damage the brain."

Soccer players head the ball six to 12 times on average during a game - and these balls can travel at speeds of over 50 miles per hour. During a practice session, players often head the ball more than 30 times.

The impact from a single heading will most likely not result in brain damage like laceration of nerve fibers, but scientists have worried that damage from repeated headings could be significant.

Dr. Lipton said "Repetitive heading could set off a cascade of responses that lead to degeneration of brain cells over time."

In order to examine possible brain injury from heading, the investigators used diffusion tensor imaging (DTI) - a modern MRI-based imaging technique - on 37 amateur adult soccer players (with a median age of 31 years), who had played soccer since childhood.

The subjects reported playing soccer for an average of 22 years and 10 months over the last year. Investigators categorized the players based on heading frequency and then compared the DTI brain images of the most frequent headers with those of the other players. Each participant also took part in cognitive testing.

DTI reveals the movement of water molecules within and along axons - the nerve fibers that make up the brain's white matter. The imaging method lets investigators calculate the uniformity of water movement (called fractional anisotropy, or FA) throughout the brain.

Unusually low FA within white matter suggest axon damage and has been previously linked to cognitive impairment in patients with traumatic brain injury.

Dr. Lipton said:

"The DTI findings pertaining to the most frequent headers in our study showed white-matter abnormalities similar to what we've seen in patients with concussion. Soccer players who headed the ball above a threshold between 885 to 1,550 times a year had significantly lower FA in three areas of the temporal-occipital white matter."

Players who perform over 1,800 headings per year were more likely to exhibit worse memory scores compared to subjects with fewer headings per year.

Dr. Lipton concluded:

"Our study provides compelling preliminary evidence that brain changes resembling mild traumatic brain injury are associated with frequently heading a soccer ball over many years. While further research is clearly needed, our findings suggest that controlling the amount of heading that people do may help prevent brain injury that frequent heading appears to cause."

Recurring head trauma in athletes has become a popular and worrisome topic. Repeated blows to the head during contact sports such as football are said to result in brain damage. The progression of the damage in athletes is characterized first by trouble focusing, followed by aggression and eventually dementia.

Friday, May 31, 2013

Studies link fatigue and sleep to MLB performance and career longevity

Two new studies show that fatigue may impair strike-zone judgment during the 162 game Major League Baseball season, and a MLB player’s sleepiness can predict his longevity in the league.

One study found that MLB players’ strike-zone judgment was worse in September than in April in 24 of 30 teams. When averaged across all teams, strike-zone judgment was significantly worse in September compared with April. The statistical model demonstrated strong predictive value through the season.

“Plate discipline - as measured by a hitter's tendency to swing at pitches outside of the strike zone - got progressively worse over the course of a Major League Baseball season, and this decline followed a linear pattern that could be predicted by data from the six previous seasons,” said principal investigator Scott Kutscher, MD, assistant professor of sleep and neurology at Vanderbilt University Medical Center in Nashville, Tenn. “We theorize that this decline is tied to fatigue that develops over the course of the season due to a combination of frequency of travel and paucity of days off.”

Data analysis tracked the frequency with which MLB batters swung at pitches outside of the strike zone during the 2012 season. Data were sorted by month for all 30 teams and compared between the first and last month of the season. Data for each team also were compared to a statistical model, based on data from the 2006 to 2011 seasons, which predicts a linear decline in strike-zone judgment per month.

Kutscher noted that the results are strikingly consistent and seem to contradict the conventional wisdom that plate discipline should improve during the season through frequent practice and repetition.

“Teams on the East or West Coast, with good or bad records, they all follow the same pattern of worsening plate discipline,” he said. “This study suggests hitters always demonstrate the best judgment when at bat in the first month of the season.”

He added that teams may be able to gain a competitive edge by focusing on fatigue management.

“A team that recognizes this trend and takes steps to slow or reverse it - by enacting fatigue-mitigating strategies, especially in the middle and late season, for example - can gain a large competitive advantage over their opponent,” he said. “This may have already occurred, as the San Francisco Giants - an outlier in the study in that their plate discipline improved during the 2012 season - went on to win the World Series.”

The research abstract was published recently in an online supplement of the journal SLEEP, and Kutscher will present the findings Tuesday, June 4, in Baltimore, Md., at SLEEP 2013, the 27th annual meeting of the Associated Professional Sleep Societies LLC.

Another study found a significant and profound relationship between the sleepiness of a MLB player and his longevity in the league. As baseline self-reported scores of sleepiness on the Epworth Sleepiness Scale increased, the likelihood that a player would be in the league three seasons later decreased linearly. For example, 72 percent of players with a baseline ESS score of 5 were still in the league at the follow-up point, compared with only 39 percent of players with an ESS score of 10 and 14 percent of players with an ESS score of 15.

“We were shocked by how linear the relationship was,” said principal investigator W. Christopher Winter, MD, medical director of the Martha Jefferson Hospital Sleep Medicine Center in Charlottesville, Va. “It is a great reminder that sleepiness impairs performance. From a sports perspective, this is incredibly important. What this study shows is that we can use the science of sleep to predict sports performance.”

Prior to the 2010 season, ESS data were collected from a random selection of 80 MLB players representing three teams. This study group doubled the sample size of Winter’s pilot study, which he presented last June at SLEEP 2012. Player status three seasons later was determined on Dec. 16, 2012. A player who was demoted to a lower league, unsigned, or no longer playing was deemed “inactive.”

Winter added that teams easily could implement sleepiness screening as part of their player evaluation system.

“I can envision simple questions about sleep being a part of the battery of tests professional organizations use to evaluate prospects,” he said.

He also noted that players and their teams could benefit tremendously if a sleep specialist diagnoses and treats the condition causing a player to experience excessive daytime sleepiness.

“That player may suddenly become far more valuable,” Winter said.

The research abstract was published recently in an online supplement of the journal SLEEP, and Winter will present the findings Monday, June 3, in Baltimore, Md., at SLEEP 2013, the 27th annual meeting of the Associated Professional Sleep Societies LLC.

Wednesday, May 22, 2013

Study challenges notion that umpires call more strikes for pitchers of same race

A University of Michigan study challenges previous research that suggests umpire discrimination exists in Major League Baseball.

The study, a collaboration between researchers at U-M and the universities of Illinois and Florida, looks deeper into the controversial argument over whether MLB umpires discriminate by calling more strikes for pitchers of the same race. It found little statistical evidence to support that claim, said Jason Winfree, associate professor of sport management at the U-M School of Kinesiology.

Winfree and co-authors Scott Tainsky of Illinois and Brian Mills of Florida, analyzed millions of pitches between 1997 and 2008 and ran the data through various statistical models. Their results suggest that findings of discrimination were questionable.

A draft of the earlier study that initially found evidence of discrimination was released in 2007 and published by the American Economic Review in 2011. National media reported on both the draft of the study and on its later publication.

In the U-M study, Winfree and his co-authors analyzed both their own data as well as that of the previously published study, but did not get consistent results when using different statistical methods and variables.

"Based on what we found, it's(discrimination) certainly not conclusive, and we could make an argument that there's actually reverse discrimination if you look only at averages," Winfree said. "Our point is (that) with something like this you want to look at the data a lot of different ways and see if you get a consistent result each time with each method. It's a pretty bold claim to say there is racial discrimination."

Winfree and colleagues found that the only specifications that suggested discrimination were when the analysis treated pitchers as completely separate players when pitching in stadiums where umpires were monitored. This seemed to drive much of the findings in the earlier study, they said.

The U-M study and others that look at discrimination in sports are significant not only for sports fans and franchises, but because it's very difficult to test for discrimination in most other occupations, Winfree said. However, because professional sports keep such detailed statistics, discrimination or lack of it is more quantifiable.

"This is a place where it's easy to test for discrimination, and if you find it here, it might be present in other work scenarios where you can't really test it," Winfree said.

The issue of discrimination among referees and umpires has raised debate in other sports as well. For instance, in 2010 the Quarterly Journal of Economics published a study that suggested racial bias among referees in the NBA.

The U-M study, "Further examination of potential discrimination among MLB umpires," appears online in the Journal of Sports Economics.

Friday, March 1, 2013

Heading a soccer ball may affect cognitive performance

Sports-related head injuries are a growing concern, and new research suggests that even less forceful actions like 'heading' a soccer ball may cause changes in performance on certain cognitive tasks, according to a paper published February 27 in the open access journal PLOS ONE by Anne Sereno and colleagues from the University of Texas Health Science Center at Houston.

The researchers tested the effects of non-injurious head-to-ball impacts on cognitive function using a tablet-based app. They found that high school female soccer players were significantly slower than non-players on a task that required pointing away from a target on the screen, but showed no difference in performance when pointing to the on-screen visual target.

According to the study, tasks that involve pointing away from a target require specific voluntary responses, whereas moving toward a target is a more reflexive response. Based on their observations, the authors conclude that sub-concussive blows to the head may cause changes specifically linked to certain cognitive functions. The authors say that the app used in their research may be a quick and effective way to screen for and track cognitive changes in athletes. They add that a tablet-based application for such quick screens may also have broader applications in the clinic or the field.

The NHL drafts the wrong players due to birthday bias

A hockey player's birthday strongly biases how professional teams assess his talent, according to a new study by Grand Valley State University researchers. The findings were published in the online journal PLOS ONE at

The research, led by Robert Deaner, associate professor of psychology at Grand Valley State, shows that, on average, National Hockey League (NHL) draftees born between July and December are much more likely than those born in the first three months of the year to have successful careers. In particular, 34 percent of draftees were born in the last six months of the year, but these individuals played 42 percent of the games and scored 44 percent of the points accumulated by those in the study. By contrast, those born in the first three months of the year constituted 36 percent of draftees but only played 28 percent of the games and only scored 25 percent of the points.

The study focused on Canadian players because in Canadian youth ice hockey there is a January 1 cut-off date. This means players born later in the year would have been consistently younger than their age group peers.

"There's no doubt that drafting professional athletes is an inexact science," said Deaner. "Plenty of sure-fire first-round picks fizzle while some late-round picks unexpectedly become stars. But our results show that, at least since 1980, NHL teams have been consistently fooled by players' birthdays or something associated with them. They greatly underestimate the promise of players born in the second half of the year, the ones who have always been relatively younger than their peers. For any given draft slot, relatively younger players are about twice as likely to be successful. So if teams really wanted to win, they should have drafted more of the relatively younger players."


Previous studies have demonstrated relative age effects (RAEs), which occur when those who are relatively older for their age group are more likely to succeed. For example, in elite Canadian youth ice hockey, roughly 40 percent of players are born in the first three months of the year while only 15 percent are born in the last three months. Although RAEs are well established in many sports and educational settings, their underlying causes remain unclear. The new study provides the most direct evidence yet that selection bias is a crucial cause of RAEs. Selection bias means that evaluators, such as teachers and coaches, grant fewer opportunities to relatively younger individuals than is warranted by their talent.

"There are many possible causes of RAEs," said Deaner. "For instance, a youth coach may mainly select relatively older players because those players' greater size means they are actually more likely to help the team. Researchers believe, however, that selection bias is also a big cause of RAEs, but there has never been a direct test of selection bias. We could make this test because we had a good measure of perceived talent, the order or slot in which each player was drafted. And we had good measures of realized talent, how long they were able to stay in the NHL and how many points they scored there. Because relatively younger players consistently performed better than would be expected based on their draft slots, we've shown selection bias."

The researchers admit that they don't fully understand the selection bias they discovered. "We don't know yet why the evaluations of NHL teams are biased, but there are several ways it could work. Because being many months older than one's peers can be a big advantage as a child or early teen, the relatively older players might be more likely to be on the most elite junior teams when they are 17 or 18, and scouts might be swayed by that," said Deaner. "Another possibility, suggested by educational studies, is an 'underdog' effect. This would involve relatively younger individuals developing better work habits so that they improve more in adulthood."

The authors believe their pro hockey results have implications for education. Deaner noted: "We have to be careful about assuming too much because a teacher deciding which children should be tracked into advanced classes is a much different situation than hockey teams assessing which adults are likely to develop into NHL stars. But, for many reasons, one would think that NHL teams should be less biased than educators. First, NHL teams are evaluating adults not children, meaning that relative age differences are proportionally smaller. Second, NHL teams are aware of RAEs, but educators may not be. Third, NHL teams have vast resources to evaluate individuals while educators do not. Fourth, NHL teams pay a steep price for poor evaluation whereas educators may not. So overall, in many situations, evaluations of ability may be greatly colored by an individual's relative age. This may even happen when the teachers and coaches know about RAEs."