Data concepts


Principles and risks of forecasting (pdf)

Famous forecasting quotes
How to move data around
Get to know your data
Inflation adjustment (deflation)
Seasonal adjustment
Stationarity and differencing
The logarithm transformation


Famous forecasting quotes

"I have seen the future and it is very much like the present, only longer."

--Kehlog Albran, The Profit

This nugget of pseudo-philosophy is actually a concise description of statistical forecasting. We search for statistical properties of a time series that are constant in time--levels, trends, seasonal patterns, correlations and autocorrelations, etc. We then predict that those properties will describe the future as well as the present.

"Prediction is very difficult, especially if it's about the future."

--Nils Bohr, Nobel laureate in Physics

This quote serves as a warning of the importance of validating a forecasting model out-of-sample. It's often easy to find a model that fits the past data well--perhaps too well!--but quite another matter to find a model that correctly identifies those patterns in the past data that will continue to hold in the future.