I've ben sent a forecast of sales from a consultancy. It uses Excel's LINEST function, taking 4 factors that seem to have affected sales in the past, and used them to make a prediction.
How do I go about adding error bars to this prediction? I believe LINEST provides a standard error, but using that would give me constant error bars, and surely the error would increase the further inot the future we go?
(Please note, I am not a statistician, so be gentle!)
Thanks!
