I have a problem consists of forecasting the next 16 values for 250 time series of daily demands, Can I forecast just for one period ahead and then multiple it by 16? is it correct? I was wondering if you give me your suggestions.

• The answer to your question is "No", unless your daily demands are all the same. IrishStat, below, lists a bunch of things that can affect time series. Also, when you say, "Can I forecast just for one period", what kind of method are you using to forecast? Commented Jan 24, 2012 at 18:37
• thank you so much for your answer, for example SES(single exponential smoothing)
– Roji
Commented Jan 24, 2012 at 18:40
• With an SES, I believe the prediction, no matter how many steps out, is a straight line, so your initial suggestion works. (Though, the prediction interval grows, so I wonder if the prediction is actually meaningful 16 values out.) I'd suggest that you need to consider the factors that Irish mentions and switch to at least double exponential (includes a trend) or triple (includes trend and seasonality, also known as Holt-Winters). Then there's ARIMA, State Space methods, ... Commented Jan 24, 2012 at 19:00
• :wayne I would never recommend assuming any particular class of an ARIMA model whose family includes all varieties of HW excepting the multiplicative variety but rather one should allow the data to speak to the model identification process. Commented Jan 25, 2012 at 14:05