The error ratio is the most overlooked statistics in football. In fact almost no data provider does report it directly. Instead they think that you need to derive it yourself using the data of the opponent. The reason is that almost all data providers measure what players do, but do not measure what players fail to do. Nevertheless, what players fail to do, is as important as what players do.

Failing to do something differs from not correctly executing what you intended to do. Of course that ratio is measured by almost all data providers. That is, for example, the ratio between all passes and all successful passes. What I mean with the error ratio is different.

First of all, I prefer to look at actual results on the field rather than action because players can perform an action correctly, but actually achieving a negative result for the team. So the first thing to do is to make a division between positive results for the team and negative results for the team. Examples of positive results are: goals, assists and getting the ball significantly closer to the opposing goal. Examples of negative results are: goals against, loss of ball control and having the opponent getting the ball significantly closer to team’s goal. 

The next step is to calculate the percentage of the contribution of each player on the pitch to both the positive results, but – and this is important – also the negative results. Once you have these, you also have the ratio between positive contributions and negative contributions. The ratio between positive contributions and negative contributions, is what I call the error ratio. So a player who has a pass accuracy of 81% – which sounds good – might at the same time have more negative contributions than positive contribution once you take into account what he fails to do.