Plus/Minus and Barcelona

New stat shows David Villa's absence may not have huge impact

Updated: December 30, 2011, 3:06 PM ET
By Albert Larcada | ESPN Insider
David VillaLluis Gene/AFP/Getty ImagesBarcelona may not miss David Villa's goal scoring as much as you would think.

Think about this question: In soccer, what is the objective of strikers?

The first thing that comes to mind is basic: to score goals. If you are scoring, you are doing your job. Goals scored is arguably the most identifiable (and available) statistic in all of soccer. It is the sexiest stat we have. The player who scored the goal in a 1-0 match is the one who will be at the top of headlines, the top of the match recap and the top of the match box score. The top goal scorers in the world are the ones you see in commercials and on the fronts of video games.

I have heard many commentators and analysts use this rationale when grading forwards. The more goals they score, the better they are playing. It makes sense and is easy to comprehend.

However, this theory is not completely accurate. Let's say Striker X scores five goals in 10 games, but the rest of his team scores none. This is a good scoring record for the player but well below average for the team. Now let's say Striker Y on the same team scores zero goals in 10 games, but the team scores 15 goals in the same time span.

Who has been a better striker for his team? I would argue the latter.

Thankfully there is a fairly straightforward way to measure this called "plus/minus". The plus/minus (+/-) statistic is tied to team performance during the time a particular player is on the field. For example, let's assume the hypothetical team above allowed 10 goals while Striker X was on the field and 10 goals with Striker Y on the field. This means that striker X has a +/- of minus-5 (five team goals scored while on the field, 10 team goals allowed). Striker Y has a plus/minus of plus-5 (15 team goals scored, 10 allowed).

Forwards have very little control over how many goals their teams allow, so a better measure for the front men is an even simpler "plus" rating -- or how many goals the player's team scores with him on the field. Setting the rating to a per 90 minutes scale neutralizes any advantage or disadvantage for a player who has played more minutes.

The +/- stat is not designed to be predictive, but a useful way to utilize it is to quantify the effect of injuries and suspensions. If you haven't noticed, there have been a lot of those in the news lately. Let's take a look at how a recent injury and suspension might affect two big name clubs in Barcelona and Liverpool.

Albert Larcada is an Analytics Specialist in ESPN's Stats & Information group. Among other analytics projects, he maintains, advances and writes about ESPN's Soccer Power Index (SPI) algorithm.