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

 A: It is common for a lot of people to assume that mathematics by itself has the answer to questions regarding "real life". While mathematics certainly does help in some cases (like telling us there is no way to cross the seven bridges of Königsberg exactly once), mathematics offers no general truth about the real world of human affairs.
It is only by defining (in mathematical terms) exactly what you mean by "how accurate", "how much wrong" etc., that you can use the tools of mathematics to answer your question.
A: It is impossible to assign a percentage score to the prediction. Speaking as a mathematician, I would have to score it as "almost as bad a prediction as possible". Your claim that "part of [the] prediction was 50% right" is nonsense.
A: You cannot measure your model's predictive power that way.
You should measure it in the long run, for example, you calculate the probability of all correct scores for any given match, for many matches, and then you could use brier score to see how well you did.
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