Example: I've got an forecast with 2000 values. Let's say they are for one year. I can group my values into months. Every month can include a different number of single values. (JAN with 200 values + FEB with 150 values + ... = 2000 values for the year )
There are two ways of calculating an error:
A) 1. Calc the errors of single values 2. Mean of this Errors (n=2000) -> Gives me the mean error, that i should use to talk about the forecast accuracy.
But what information do i get using the following way:
B) 1. Mean of the single values per month (n = various) 2. Calc the error of the mean per month 3.) Sum up the mean again (n=12)
Would it be the same?