Editing Forecasting (section)

===Drift method===
A variation on the naïve method is to allow the forecasts to increase or decrease over time, where the amount of change over time (called the [[Stochastic drift|drift]]) is set to be the average change seen in the historical data. So the forecast for time <math>T+h</math> is given by

:<math>\hat{y}_{T+h|T} = y_T + \frac{h}{T-1}\sum_{t=2}^T (y_{t}-y_{t-1}) = y_{T}+h\left(\frac{y_{T}-y_{1}}{T-1}\right).</math>  <ref name="otexts.org"/>

This is equivalent to drawing a line between the first and last observation, and extrapolating it into the future.