ANALYSE THIS: PSG more likely to progress than historic results suggest

FOOTBALL – The Champions League first legs have all been played and the favourites to progress generally look in good shape to do so. There are two common ways to assess what the likelihood of going through actually is – the first uses historical results and calculates the frequency with which teams recording a particular result went through. The second uses a statistical model based on team ratings to assess the chances of progress. The two methods give broadly the same chance for each of the four ties won by the away team but if a match is drawn or results in a narrow home win, the chances from the two methods begin to diverge.

Real Madrid, FC Barcelona, Manchester City and VfL Wolfsburg all won their away first legs and all are almost certain to progress to this year’s last eight. Basing their chances purely on the historic frequency of the scoreline gives them all around 97% or more chance of a quarter-final place. Taking account of the relative strength of these teams and their opponents, using the Euro Club Index, doesn’t produce much of a difference with all still being given over 90% chance of progress.

If first leg matches are drawn or result in narrow home wins though, an approach using the relative quality of the competing teams comes into its own. Take Paris Saint-Germain’s 2-1 win against Chelsea as an example. Using historic results, that narrow defeat gives Chelsea slight favouritism to make the last eight, a reasonable conclusion if the two teams were evenly matched. The problem with this however is that Paris Saint-Germain have a much stronger team than Chelsea. This is illustrated by the current Euro Club Index ratings which have the French club fourth and the English champions 11^th.

 More importantly, there is quite a difference in the ratings of the two clubs with Paris Saint-Germain given a Euro Club Index of 3874, more than 500 points more than Chelsea’s 3317. Taking the relative quality of the two clubs into account in this way makes Paris Saint-Germain strong favourites with around 74% chance of going into the quarter-final draw.

Using historical results can be a good quick rule of thumb to get an idea of the chances of progression after the first leg of a tie has been played. Close matches in which the home team doesn’t lose can produce a biased result though and in those cases in particular, it is better to use a statistical model which takes the quality of the teams into account.