Saturday, 14 January 2012

Thierry Henry.A Deal Well Done?

Arsenal welcomed back an old familiar face on Monday and Thierry Henry immediately repaid their faith in the former spearhead of their strike force with the winning goal at the Emirates against Leeds United in the 3rd round of the FA Cup.Signed as cover for Arsenal's less than prolific departees for the African Cup of Nations,Henry's reappearance in the EPL after two season's in the MLS provides an intriguing real life experiment.

How for instance will the formerly prolific scorer cope in the EPL now that he's into his 34th year?

Quantifying a player's level of performance in a predominately team sport such as soccer is certainly problematical.A whole raft of new measurements are slowly being recorded,although their availability and how they are interpreted and applied to individual players is still up for debate.Fortunately Henry in his time at Arsenal was predominately a goal scorer and goals scored are easy to record and can be used to readily define the course of a player's career.A goal scorer who stops scoring goals doesn't stay around in the EPL for long.

Henry became during his time in the EPL a member of an exclusive club of players who scored 100 or more Premiership goals,a feat that singles those players out as being not only potent finishers,but also having the longevity to play at the top for multiple seasons.The 100 club contains around twenty current members and we can use their combined goals scoring records to devise an ageing pattern for their exploits as a group.

Goals scored per game does a good enough job at rating a goals scorers ability,however it does tend to favour players who were on teams which scored lots of goals.Therefore I usually express a goalscorer's core statistic in terms of his goals per game rate as a proportion of his team's goals per game rate as this gives a little more context around the kind of goal scoring environment the players was performing in.It also helps to highlight how integral a player was to the team's overall goal grabbing ability.For example if  player scores on average a goal a game for a team which scores on average 2 goals a game,his scoring rate is half that of his team.If his team scores 3 goals a game,his rate is only a third.

To see how elite goalscorers age I recorded the cumulative,team adjusted,scoring rate for all members of the EPL 100 club and plotted the results.The sample is obviously biased because not only does it contain only the league's very best finishers,but it's also biased towards longevity.But we are interested in trying to predict a likely ageing curve for Thierry Henry and he is very much typical of the kind of player who makes up the larger sample.The curve wouldn't necessarily apply to goal scorers as a group or indeed outfield players as a group.

Scoring Performance Curve for All Time Elite Strikers in the EPL. 

As you'd expect,players who stay around the EPL long enough to net at least 100 career goals are performing to a high level at a young age,peaking at around 25 years of age,but are still playing at a similar standard as they enter their thirties as they did when they were just 20.Once into their thirties though,their overall scoring contribution to the team begins to decline with increasing steepness and also remember this graphic does not account for appearances made by the player,just his average scoring rate when he does make it onto the field.So although the graph may capture how injuries impact on a players ability to score goals,it doesn't tell us anything about how injuries can limit playing time.So older players may appear more attractive because of the omission of game time limiting injury data.

The profile of the plot does tells us that typically an elite striker is performing as badly as he has ever done by the time he reaches his 32nd birthday.They are still productive,but they no longer have any upside in terms of resale value or increased goal getting capacity.Scoring capacity then declines rapidly as does sample size as players in the sample drop down in grade or out of the game completely.

So lets now see a similarly plotted graph looks like for Henry.He spent five years at Monaco,before making a mid season switch to Juve,where he played mostly in a wide attacking role,before joining Arsenal in 1999.

 Scoring Performance Curve for Thierry Henry for Arsenal. 

The plot is understandably much less tight as we are now dealing with smaller sample sizes relating to just one player,but the general shape of the line of best of is very reminiscent the plot for elite strikers as a whole.Notably Henry's average seasonal scoring rate compares more favourably with that of his team than does the team adjusted average for strikers as a whole over the same stretch of years.An impressive personal statistic for Henry,especially because he played at least 30 times in each season except his last one.He also peaked a couple of years later than was usual for his contemporaries,possibly as a result of playing initially in less physically demanding leagues or possibly as a trait of Henry himself.By his last season his career curve was beginning the downward curve typical of the group,his appearances where almost half their number when he was at his peak,but he was still playing and contributing at levels that well exceeded the expected norm.This set of exceptional figures,whilst combined with a fully expected onset of inevitable decline goes some way to explain why Arsenal firstly chose to sell Henry and secondly it shows how they were able to demand such a large transfer fee from Barca for a player approaching his thirties.It also fully justifies the decision to honour him with a statue.

So what can Arsenal fans expect from their returning star of yesteryear.The deal is merely a short term loan period,so there aren't any issues surrounding Henry's declining ability to play out an entire season.He played over 30 total games in each of his three seasons at Barca and has since managed almost 40 games in the less demanding MLS.So he should easily manage a short loan period.It's likely that his effectiveness will be limited simply by his ageing curve.

Throughout his EPL career,Henry's contribution to Arsenal's scoring was on average 30% higher than those of a typically elite striker,therefore if we input his age to the line of best fit for all strikers and increase that value by 30% we will  get a reasonable approximation of where Henry's ability currently resides.A 34 year old top striker who is still good enough to be still playing in the EPL will be scoring around 18% of the total scoring rate of his team.If we include the "Henry" premium that rises to about 24%,the equivalent rate for an elite striker who is still just the right side of 30 and not approaching his mid thirties as Henry is.If we now use Arsenal's average rate of goalscoring over the season we can deduce that Henry should be able to score an average of 2 goals for every 5 appearances he makes.

The amount of games Henry will play during his loan period will make it virtually impossible to conclude if he has performed to his predicted level,but the mere fact that Wenger has done the deal means that more analytically talented football brains than this one consider Thierry well worth a punt.

In a follow up post I'll include career curves for more members of the 100 club and reveal which current EPL strikers is a real one off.

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