Did the Celtic Transfer Ruin Dundee United’s Season?

Seth Dobson , takes a look at why The Arabs have suffered a severe slump in form, or have they?

By now you probably know that Dundee United are pish!

One of the narratives that has developed around the Terrors’ recent decline in form focuses on the transfer of Stuart Armstrong and Gary Mackay-Steven (hereafter, SAGMS) to Celtic in January. This is a reasonable hypothesis since SAGMS were arguably United’s two best players. However, as with any reasonable hypothesis, it needs to be tested against the data. In this post, I take a look at some team performance metrics for Dundee United before and after the transfer deadline.

I will focus on three main variables:

  • Shots on Target Ratio = Shots on Target For/(Shots on Target For + Shots on Target Against)
  • Score Rate = Goals For/Shots on Target For
  • Save Rate = Goals Against/Shots on Target Against

Score Rate and Save Rate are typically combined into a single metric called PDO:

  • PDO = 10*(100*Score Rate + Save Rate)

Shots on Target Ratio (SoTR) and PDO are the two main determinants of goal dominance, as the figure below shows.

Goals Ratio is effected by SoTR and PDO. But SoTR has a stronger relationship to future points.

Click to Enlarge

As you can see from table 1, all three metrics have declined since the SAGMS trade, but the one that has declined the most is Save Rate.  Save Rate, of course, has little if anything to do with SAGMS.  Thus, from a statistical perspective, we must conclude that the transfer of SAGMS to Celtic is not the only or even the most important reason for Dundee United’s recent woes.

So who is to blame?

There is an emerging view that Jackie McNamara is at least partially at fault. However, the data do not allow us to draw this conclusion unequivocally. Both SoTR and PDO have declined; the latter more so than the former. But PDO has an inherent volatility to it. SoTR is comparatively much more stable. Normally I would blame the manager for a drop in SoTR, because I believe it’s the manager’s job to prepare his team to create a higher % of chances than the opposition. But losing SAGMS could explain this drop.

As far as PDO is concerned, most analysts agree that managers in general should not be judged, positively or negatively, on PDO because of its inherent volatility. For example, I have written elsewhere about United’s improbable Score Rate through 26 matches this season. United’s Score Rate was likely to regress whatever happened because a rate of ~40% is unsustainable even for the best clubs in the world (most hover around 30%). So, while it’s clear that the SAGMS transfer is not the main reason for Dundee United’s recent decline, it’s not clear to me that the manager should take blame, statistically speaking.

Sometimes in football, as in life, no one is to blame.

Should Jackie Mac get the Sack? If so, why so? Comment below or tweet us @90minutecynic

Follow Seth on Twitter: @226Blog and fitbafancystats.blogspot.com

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