# Accuracy of football prediction

Say you predicted that Brazil would have beaten Germany 2-1, by how large a percentage were you wrong?

As Brazil scored 1 out of 2 goals, you could say that part of your prediction was 50% right. However, as Germany scored 7 times the number of goals, that's less accurate. On top of this, the combination of the two scores has me perplexed and any help would be much appreciated.

To summarise, how accurate is your prediction given the following:

Predicted Score: Brazil 2-1 Germany
Actual Score: Brazil 1-7 Germany

• On a more mathematical basis, a percentage describes the number of possible "good" outcomes divided by the number of total possible outcomes. To define "how large" you were wrong, you need to define "good" and most importantly "outcome", and then give weights to each outcome. This can be done in many different ways, and choosing one is up to what you want your percentage to represent. – Patrick Da Silva Jul 12 '14 at 21:38
• ... Secondly, thanks for the more mathematical answer. I am trying to calculate how close the "correct score" prediction was to the ultimate actual score. If that can be expressed in percentage terms... (ed ajf) – Dan Jul 12 '14 at 21:47
• My answer was essentially "mathematics alone canot tell you the answer". You have to decide what you want this percentage to mean. Do you want it to explain how badly the number of goals of Brazil was wrong? How the goal difference Brazil-Germany was wrong? (i.e in the 2-1 B/G it is +1, in the 1-7 it is -6), do you want the quadratic error as in statistics? There's no preferred option. Personally I'd like to say that since the predicted score was Brazil +1 and the actual score was Brazil -6, I'd like to say that this was 600% wrong, but then again, it's personal. – Patrick Da Silva Jul 12 '14 at 21:59
• I suspect many people would agree that a prediction of 1000-1 for Germany is closer than one of 1-0 for Brazil. – Théophile Jul 12 '14 at 22:53