Topic summary
Differencing
Extracted from the Wikipedia article Autoregressive integrated moving average.
Differencing
A stationary time series's properties do not change. Specifically, for a wide-sense stationary time series, the mean and the variance/autocovariance are constant over time. Differencing in statistics is a transformation applied to a non-stationary time-series in order to make it trend stationary (i.e., stationary in the mean sense), by removing or subtracting the trend or non-constant mean. However, it does not affect the non-stationarity of the variance or autocovariance. Likewise, seasonal differencing or deseasonalization is applied to a time-series to remove the seasonal component.