Thus, based on past sales, the estimate for 2008 is $16.5 million. In this time series example, there were five years of sales data. Based on those five sales figures, we estimated sales for 2008. Many researchers suggest that we do not project sales, production, and other business and economic series more than n/2 time periods into the future where n is the number of data points. If, for example, there are 10 years of data, we would make estimates only up to 5 years into the future (n/2_10/2_5). Others suggest the forecast may be for no longer than 2 years, especially in rapidly changing economic times.