Wayne Rooney’s worth in goals

Rooney's goals have been less valuable this season (Image: Flickr/Joscarfas)

Not all goals are the same, this much we know as football fans. Man United’s fifth goal against Wolves on the weekend, for example, clearly has less value than Ryan Giggs’ late winner at Norwich last month.

Soccer Statistically has provided a way of quantifying the value of goals through an outcome probability calculator. By inputting a scenario from any given match, we can evaluate the effect of a goal on win, draw and loss probabilities, based on previous Premier League matches.

For example, a home team taking the lead in the 60^th minute increases their chances of winning from 34% to 81%, and decreases the odds of a draw from 45% to 15%. We can assign a point value to this goal; the expected points at 0-0 was 1.47 [(0.34 x 3 points) + (0.45 x 1 point)], but at 1-0 the expected points total is 2.58 [(0.81 x 3) + 0.15]. Hence the expected points added (EPA) is 1.11 (2.58 – 1.47).

The Power of Goals blog has done a lot of work on illustrating the effect of goals of expected points, for example in Manchester City’s home win against Tottenham in January. We see how Man City’s two-goal lead almost assured them three points before Spurs’ quick double strike evened things up. Balotelli’s late converted penalty shifted City’s expected points total back up to three again. His goal was worth nearly two points, turning a near-certain draw (1 point) into a near-certain win (3 points).

Soccer Statistically has put together a list of the players who have contributed the most to their teams this season in a Premier League Expected Points Added leaderboard. Unsurprisingly, Robin van Persie leads the way, followed by the likes of Ba, Yakubu and Lampard.

I was surprised to find that whilst Wayne Rooney has scored 20 goals this season, his goals haven’t been all that valuable. On average, each goal has been added 0.34 expected points to the team, compared to van Persie’s 0.82, or Lampard’s 0.90. This average is also known as the average goal weight (AGW), and is the player’s EPA divided by the number of goals he has scored.

An early accusation that could be levelled at Rooney, therefore, is that his tally for the season is inflated by ‘easy’ goals in foregone conclusions. He’s certainly down on last season, when his AGW was more than double than it is this campaign. His EPA from goals is also lower, despite scoring nine more than last season.

It’s fair to suggest that Rooney’s contribution directly in front of goal has been less valuable on average this season, though his assists have been marginally more important compared to 2010-11.

Comparing Rooney to his team mates from the last two Premier League seasons provides some context. The tables may not be the easiest to process without options to sort columns, but hopefully illustrates where he ranks in the side. (Both tables show only players with three or more goals/assists. Assists are taken from the Premier League website, and excludes those for penalties and own goals).

Rooney has United’s third-bottom AGW, though he ranks fourth-highest in average assist weight (AAW). That’s not to say Rooney doesn’t score important goals, more so that meaningless strikes have diluted his apparent value to the side. The same can be said for Berbatov, Nani and Hernandez this season in a free-scoring United team. Robin van Persie has not had the same luxury at Arsenal.

At the same time, it’s worth keeping an eye on Rooney’s contribution to the Man United. Last season the vast majority of Rooney’s assists came with the team two or more goals up, whereas 2011-12 has seen him produce three of his four most-important assists in the last two years.

Meanwhile, 13 of his 20 goals this season have ensured a two-goal cushion or more, with 9 of these goals to give leads greater than 2. Last season, 8 of his 11 goals were equalisers or gave United the lead.

Ultimately this may be a reflection of the fact Rooney has been employed as deep as central midfield this season, and is perhaps more involved in the build up as opposed to finishing of more important goals.

So is Rooney less valuable to Man United than he has been before? It’s unlikely. The next step would be to analyse what he’s doing differently in midfield to get a gauge of his worth to the team.

All EPAs calculated using Soccer Statistically’s outcome probability calculator. Whilst it does not account for all factors in a football match, for example the strength of the opposition, it is at least consistent for this analysis.