Quantifying the Lack of Opportunities for Trainees in the Premier League

A dying breed

I made the following statement in my recent piece on The Tomkins Times studying the correlation between table position and squad transfer costs.

The data shows that the Premier League averaged only 2.6 homegrown players per match (24% of the players on the pitch) in its inaugural season. Since then, it has been on a steady erosion of about a tenth of a player per game per season to the point of being under a player per game (8% of players on the pitch) by the 2009-2010 season. By comparison, the average percentage of a squad composition of youth players bounced between 15% and 20% the last ten seasons, meaning that homegrown players are getting very few shots at playing time. In fact, the difference is considered “extremely statistically significant” when the proper statistical tests are performed, which is a rarity in the sports statistics world.

What does the "extremely statistically significant" difference translate to in terms of squad and on-pitch opportunities?  To quantify this I looked at the percentage of squads and players on the pitch that were classified as trainees during each season in the Transfer Price Index database.  Luckily, those two data sets and the difference between them were normal and their variances equal, so I was able to use a paired t-test to quantify whether or not there was a difference and how big it was.  A nifty online calculator for t-tests can be found here.

The summary of the two data sets is shown below.

Running a paired t-test returns the following results (click to enlarge).

The projected mean difference is 5.333, while the extreme low prediction is 4.731 and high is 5.936.  This means there is an average 21%-27% gap in trainee representation on the pitch versus their representation on the squad.  This translates, on average, to about 1 in 4 trainees who will not see any action in a season.  By the latest seasons, it had ballooned to nearly 1 in 2 trainees.

It appears as if there is not only a pull from teams to buy transfers, but also a push by trainees to look for opportunities elsewhere and thus lose their trainee status and contribute to the high proportion of transfers - free or otherwise.