An Accidental Statistician: The Life and Memories of George E. P. Box

“What do you know about this business?”

Chapter Eight

Time Series

During the 1960s I had begun to work on four books that I wrote with five good friends. Norman Draper and I wrote on evolutionary operation, the one book that was published before the decade was over.¹ The second and third books were begun with Gwilym Jenkins and George Tiao, respectively. The fourth, which had the longest gestation period of the four, was Statistics for Experimenters with Stu Hunter and Bill Hunter.

When I studied statistics at University College, I remember taking a course on time series. It was all very theoretical, and at the time, I did not see that it had much practical use. Much later, at ICI, I was mostly working on experimental design, but there was a group there from the Intelligence Department that forecasted monthly sales. This involved a panel, one of whose members, for example, knew about the demand in India for indigo, another was an expert on Chinese requirements for certain other dyestuffs, and so on. The forecast was arrived at by putting together the opinions of these individual experts. But when I compared their monthly forecasts with what actually happened the following month, I had doubts. The differences between their forecasts and what happened were the forecast errors, and I reasoned that if the forecasts were good, their forecast errors would be unforecastable from past data. I found that for the Intelligence Department's forecasts, this was not true. I went back over the ...