Attacking & defensive effectiveness, incorporating form

Introducing form-weighted averages

When updating the attack and defence effectiveness graphics throughout the season, I’ve been increasingly mindful of the need to incorporate a team’s form into any analysis of their performance. Now that we’re over halfway through the season it seems a bit of a stretch that the average values that drive the graphics give equal significance to a team’s first game of the season as to their most recent match.

After a bit of tinkering, I settled on using a simple weighting curve like this one to assign proportionately more significance to more recent matches.

weight curve

On the horizontal axis we have the 46 league games in a season, stretching backwards through time,  and on the vertical is a weighting factor.  The idea is that the further into the past a match occurred, the contribution any of its data (e.g. shots taken) make to overall averages decreases via a simple weighted average calculation. Calibrating this curve has been a matter of trial and error, but I’m reasonably happy with how it’s working in practice.

It’s worth noting that this is still some way from a ‘perfect measure’ as there are plenty of other factors which can impact on a club’s performances – such as the relative difficulty of a run of fixtures, injuries to key players and of course luck – but this feels like a step in the right direction.

I’ve chosen to incorporate the additional measure by adding a second, smaller bubble to the graphics for each club. While the larger, bolder bubble continues to show the traditional ‘flat average’ for the entire season, another smaller, fainter one connected by a dashed line shows the ‘form weighted’ average. Think of the smaller bubbles as a more relevant measure of how each team is performing at the moment.

As always, charts can be enlarged in a separate tab by clicking on them and I’ll provide some sample observations for each one.

Championship

Att Eff CH 090213 form

  • While Ipswich and Barnsley have been the division’s most wasteful sides overall they’ve been sharper in front of goal lately, while the reverse is true of Millwall and Hull who’ve recently struggled to convert their chances.
  • Brighton look to be focusing on creating fewer, better chances, while Leicester look to be heading in the opposite direction and throwing everything at their promotion push.
  • The effect of Huddersfield‘s poor recent run is clear too – at the moment their attack is looking the division’s least dangerous.

Def Eff CH 090213 form

  • Defensively we can see the effect of Cardiff‘s strong recent record, while beneath them on the graphic Blackburn have started to tighten up under Michael Appleton.
  • It’s all a bit cramped in the middle of the graphic, but you can see that both Sheff Wed and Ipswich are also restricting their opponents’ chances more effectively of late.
  • Leicester‘s increased attacking emphasis looks to be leaving them a bit more open at the back, although they seem to be soaking up the extra chances reasonably well.

League 1

Att Eff L1 090213 form

  • The screamingly obvious thing to focus on here is how profligate Preston have been lately, while Tranmere and Notts County have also struggled to find the net as reliably as they once did.
  • Swindon and Coventry look to be shooting more regularly as the promotion race hots up, while at the other end of the table both Hartlepool and Scunthorpe are making better use of their chances.

Def Eff L1 090213 form

  • Swindon have been setting the standard in defensive resilience lately, even by their own high standards, while BournemouthBury and Yeovil have shown similar improvements in dealing with the shots they face.
  • It’s all going wrong at the back for MK Dons who are much easier to breach at the moment, while Portsmouth‘s decline is also clearly visible.

League 2

Att Eff L2 090213 form

  • Accrington have struggled in front of goal lately and their profligacy is plain to see here, while Bradford and Gillingham are also finding the net more elusive at the moment.
  • Rochdale‘s attacking approach is looking increasingly ‘scatter gun’ but Bristol Rovers are enjoying a relatively deadly spell in front of goal.

Def Eff L2 090213 form

  • Barnet‘s defence looks to be toughening up significantly, while Exeter and Burton also look more solid at the back lately.
  • While Gillingham have been consistently tough to score against all season, Southend are increasingly formidable – their impressive goal difference could make all the difference as the promotion race plays out.

Next steps

Depending on how they’re received, I’ll continue to plot the form-adjusted bubbles on these charts going forward, as to me it makes more sense than arbitrarily choosing a point in time to show a movement from like I did for previous updates. The aim for the rest of the season is to provide a weekly set of fixture previews and then follow up with updated versions of these graphics after the matches have been played, with the commentary I provide focusing more on interpretation than explanation.

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