Recently I’ve written two posts, comparing the distribution and variance of points in the Premiership and La Liga. This is a quick book end to those pieces – a comparison of how strongly goals and points are related in the two leagues.
So firstly the Premiership, I’ve put up this plot in previous seasons but the data-set has expanded since then:
So two things – the correlation is incredibly strong, and the equation of the best fit line suggests a goal is worth roughly two thirds of a point. Determining how much a goal is worth in terms of points isn’t quite this simplistic (and it’s something I’ll be having a go at in the near future) but this is a solid benchmark for now.
So how does the equivalent plot look for La Liga? Thanks, once more, go to Infostrada, through the ever helpful Simon Gleave, for providing me with historical La Liga tables (Infostrada can also be found through their website here).
Once more there’s a strong correlation, if a little weaker, between goals and points, and a goal is suggested to be worth ~0.03 fewer points than in the Premiership.
How can we explain the discrepancy? Well for one thing in this dataset (240 team seasons for each plot) there are ~2% more goals scored in La Liga than the Premiership and it makes sense that the more goals there are scored, the fewer points they are worth – think of how much an individual basket is worth in basketball for example.
Do these numbers seem to be in the right ballpark? Well lets take the simplest of terms and use hockey as an example, where it’s generally accepted that a goal is worth about one third of a point. There’s roughly twice as many goals in hockey, and 15% fewer points (~2.3 vs ~2.7) – so it seems reasonable that a goal in football would be worth ~twice as much as a goal in hockey, and that’s what we see here.
As for why the correlation is lower in La Liga I’m not totally sure, and open to suggestions, but I think it has something to do with the more crowded mid/lower end of the table in La Liga, which was first highlighted here and is also evident if you compare the two plots above.
Finally, how many points would we expect a team to have scored over a season in the two leagues if we knew its final goal difference?