12.6 Backcasting

Sometimes it is useful to “backcast” a time series — that is, forecast in reverse time. Although there are no in-built R functions to do this, it is very easy to implement. The following functions reverse a ts object and a forecast object.

Then we can apply these functions to backcast any time series. Here is an example applied to quarterly retail trade in the Euro area. The data are from 1996-2011. We backcast to predict the years 1994-1995.

Backcasts for quarterly retail trade in the Euro area using an ARIMA model.

Figure 12.6: Backcasts for quarterly retail trade in the Euro area using an ARIMA model.