Friday 9 November 2012

Edin Dzeko Is Not a Super Sub.

Super sub is an uneasy and often unwelcome crown to wear, with the juxtaposition of a superlative with a faint hint of failure. Liverpool's David Fairclough provided the benchmark by which all other lethal replacements are measured, making his name in the late 70's and early 80's during an era when domestic substitutes were singular and always wore the number twelve shirt. 37 goals from 92 starts and 18 from 62 from the bench hint at the lopsided nature of his goalscoring exploits that ensure he is fondly remember by football fans from the seventies and not just on Merseyside. Ultimately his misfortune was to straddle the careers of first Toshack and Keegan and then Dalglish and Rush.

The attractive narrative of the super sub is easy to appreciate. Dramatic match winning strikes live long in the memory and most substitutes manage to stay on the pitch to feature in many such goals. Ole Gunnar Solskjaer's 93rd minute winner against Bayern Munich in the Nou camp in 1999, twelve minutes after his introduction. Fairclough's reputation making winner in the 84th minute against St Etienne in an earlier incarnation of the same competition and Moses' late header a few days ago are just a few such efforts that understandably eclipse the much more numerous failed substitutions. "Not so super sub" doesn't quite have the same headline appeal.

Bosnian, Edin Dzeko is the current poster boy for the super sub with an eye catching recent run of scoring form from the bench, combining quantity with game changing late strikes. You can read a typical appreciation of Dzeko's supposed qualities on the BT Footballing Website written by journalist Rob Smyth.

Helpfully the statistics appear to back up the narrative that Dzeko is much more effective as a late, game changing introduction rather than as a starter. He's made over 40 starts for Manchester City since his arrival, comprising over 3,700 playing minutes during which he's scored 19 times at a rate of a goal every 195 minutes. Contrast this with his forays from the bench when his 30+ substitute appearances, lasting just over 600 minutes has yielded 12 goals at a rate of a goal every 52 minutes.

Undeniable evidence ?

Unfortunately, the evidence fails on two crucial counts. Firstly, "super sub Dzeko" is playing in a very different goals scoring environment than is "starting Dzeko". Scoring in football becomes almost imperceptibly more frequent as a match progresses, with 45% of the goals coming before the interval and 55% after half time. We can demonstrate these different scoring environments by looking at a typical breakdown of goals for the first ten minutes of an EPL game (when "starting Dzeko" will almost certainly be on the field) and the final ten minutes (when "super sub Dzeko" will be present).

The first ten minutes is more likely to be goalless than the last ten and the former is also significantly less likely to contain exactly one or two goals than is the final ten minutes of a game. As a substitute, Dzeko averaged 18 minutes per game, so he was consistently playing when goal scoring was approaching a peak, not just for him but also for the team as a whole. Therefore, to look at his scoring exploits from the bench within the context of his scoring environment we need to compare his scoring record with that of Manchester City as a team for the time he was on the pitch as a substitute. And also repeat the exercise for Dzeko as a starter.

Goals By Dzeko As A Starter. Total City Goals Over Same Timescale. Goals By Dzeko As A Sub. Total City Goals Over Same Timescale.
19 74 12 32
26% of Total. 37% of Total.

Initially the evidence still appears strong, although not quite as extreme as the figures based on raw minutes per goal in Dzeko's role as a starter and as a sub . As a substitute Dzeko scores 37% of the goals that City score while he is present in that role, but just 26% when he starts. However, we are now faced with a second problem if we try to take these figures at face value. Dzeko's super sub status is based on just 600 minutes of playing time, a fifth the size we've used to measure his scoring rate as a proportion of City's overall record as a starter. And small samples often lead to extreme, but unreliable estimates.

Dzeko's 600+ minutes as a sub is almost exactly equivalent to the number of minutes he played as a starter in his first eight games of the 2011/12 season. During those matches he scored 7 of the 17 goals recorded by City, 41% of their goals. A number in excess of his super sub strike rate, but a poor indicator of his career figure of 26% based on a larger sample size. If his hot start to 2011/12 wasn't indicative of his career figures, shouldn't his 37% strike rate as a sub, collected under very similar playing time also carry a caveat ? 

Dzeko obviously doesn't relish the tag of "Super Sub", but the good news is that sample size and differing goal environments indicate that he probably isn't one anyway (even if they exist). In fact for a more extreme example of the "art", he need merely look across his own attacking line to Sergio Aguero, who has scored over 50% of his team's goals as a substitute on an even smaller sample size of 300 minutes. 

In short, City have an embarrassment of attacking riches and if you cut the sample small enough extreme results are bound appear. Add a persuasive narrative and you've recreated a long lost story from the seventies. 

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