Forecasting difficulties
Brace yourselves: econometrics follows. Look at this time series. What happens next? Many macroeconomic time series look a bit like this. They are trended, but wobble around in interesting ways compared to that trend, and for long periods of time. You can see that by eye — and it’s even clearer if you put the series on a log scale, thus: How would you go about forecasting this time series? Well, you might start by estimating the trend in