Thursday, 1 June 2017

Lawro: Master Bayesian

With another season over I wanted to look again at the accuracy of Mark Lawrenson's predictions in the Premier League.  I've been doing this for a number of years now, starting with an analysis of the 2012/13 season and I'm always amazed at how well he does.

At face value, Lawro's table based on his weekly predictions for the BBC look a bit ridiculous, not least his prediction that Liverpool would go through the season unbeaten:
League Table of Lawro's predictions (via BBC Sport)
If you'd used his selections and placed £10 on his predicted result (Home/Draw/Away), you'd have made £501.50 profit from 368 matches (I've excluded the 12 rearranged games) and actually made a small £7.45 profit on his Liverpool predictions.

Lawro's 92 points prediction for Liverpool may seem a bit extreme but you have to consider that this is built up from a series of individual predictions rather than a single prediction of their points total.  In any single game it may make sense to not predict Liverpool will lose (even if you put aside the fact he's an ex Liverpool player).

I previous years most of Lawro's profit has been derived from sitting on the fence more than the average punter and taking advantage of the fact that draws are often overpriced as people in general want to back a winner rather than a stalemate.

This year however, his profit (and I'm sure what has been a bit of a hit on the Bookies in general) comes from the fact that the bigger teams have got their act together and this season has very much been a two-tier league (or 3 if you consider Everton in no-man's land on their own).

If I had to summarise what I thought made Lawro successful all these years, I think it's the fact that he isn't too swayed by short term noise and to some extent you could largely predict his predictions from early on in the season (not least the scorelines used)

For years now, Lawro's kept a pretty simple system and almost always predicts a draw as being 1-1 rather than 0-0 or 2-2, as mentioned in previous years this makes sense as it makes you more likely to be closer to the true result as although betting wise predicting 1-1 when a match finishes 2-1 is no closer to being right than predicting 0-0 it 'feels' closer
The difficultly of any prediction system or model is how much to weight the recent past vs. more historical data. e.g., Is form over the last 1/3/12 games more predictive than what happened last season or even further back.

A great example of this would be Leicester, although a serious title defence was always going to be incredibly unlikely, their results under Ranieri could also be considered to be somewhat surprising.

Obviously clubs don't work in a vacuum and changing managers impacts things (both positively and negatively I can tell you as a Swans fan), but trying to judge whether something is an outlier or the new normal is hard.

People often talk about things 'regressing to the mean' but the whole issue with that is it assumes you've predicted the right mean to start with but as Lawro's predictions have proved over the years, having an opinion and sticking with it isn't the worst strategy in the world.

I'd like to thank MyFootballFacts for collating the Lawro results each week and for collating results and betting odds, both are great resources.

It's still a work in progress but I've used the info from the Football-Data site to create an interactive dashboard of shots taken/faced by each team:

Twitter: @we_r_pl

Saturday, 13 May 2017

Llorente: Lion King

With just 2 games left, it's going to require a huge team effort to get over the line and although I'd love to think we'll be safe by Sunday afternoon, I think it'll go down to the final game. One of the key things that's even kept us in with a chance is the goal scoring of Fernando Llorente.

Over the course of his career, Llorente has focused on doing his work 6-10 yards out from goal which is a large reason why any criticism of his sprint stats is misguided. As with any stat, context is king and Llorente's relative lack of sprinting isn't the sign of a lazy player, more one who is doing what he's good at and what he's been told to do. If you used him for an aggressive press you'd end up with the worst of both worlds, it wouldn't be very effective and you'd also then knacker him out making him less effective.

Llorente's shot location in the League games over the last 5 seasons, focused on the danger zone
For the Swans, the location map is pretty similar, he has 13 goals from his 50 shots with anything long range at a minimum:
Majority of Llorente's activity is within 10 yards of goal
Not surprisingly, an awful lot of that shot activity are headers with 35 of Llorente's 50 shots (and 7 of his 13 goals) coming via his head.
Opta have reclassified his goal v Everton as 'Other Body Part' but I'm keeping it as a header
Llorente using his head a lot is no big surprise but the fact that 70% of his attempts were headers actually puts him quite a way out in front of 'similar' players (Rondon 42%, Benteke 47% and Crouch 50%), also no surprise that he has more headed shots than today's opponent Jermain Defoe but was interesting that 0 of Defoe's 96 attempts have been headers.

One thing that should be highlighted though is the comparison with Llorente's fellow Spaniard Baston. Looking at things now, Llorente seems a massive success (and supposedly coveted by Chelsea during the Jan transfer window) and Baston a flop.

Comparing their figures though, Baston has scored 1 goal in his 549 Premier League minutes. The fact that those minutes are spread across 18 games (athough only 4 starts) makes it feel as if he's had plenty of chances and not taken them.

As a comparison, in the first 549 league minutes Llorente played, he also scored only 1 goal. You could argue it's taken time for Llorente to settle in and for the team to work out how to make the most of him but surely you could put the same case forward for Baston.

Whether he'll come good at some point is difficult to tell but certainly too soon to write him off, even if this season (at least so far) has been a bit of a waste for him.

Opta Data via Statszone, Whoscored  Squawka