One of the most difficult areas of forecasting is in dealing with time series. Our profits have been x, y, and z over the past three years, so what will they be next year? Unfortunately, we might say, this is perhaps the area where forecasting is most necessary in the business and commercial world. In the United Kingdom, and probably elsewhere, documentation involving the sale of shares and other investment products has to carry the warning “past performance is no guide to future performance.”
The problem is essentially to forecast data relating to the next time period from knowledge of the data from previous time periods. In Chapter 14, I explained the technique ...