I have 12 months of in-sample data and 12 months of out-of-sample data. I'm trying to calculate the scaled error for an h-step ahead forecast where h=1, 6 and 12. Do I just calculate the error at each of these points and divide each by the average of the in-sample observations, or is there a summation involved? For example, if the out-of-sample values are
1,3,5,3,4,6,7,8,2,1,4,5) and the forecasts are (2,3,6,3,4,8,6,4,1,7,3,9), the errors are (-1, 0,-1,0,0,-2,1,4,1,-6,1,-4) What would be the 6-step-ahead error?