But anyone looking to make a decision on the basis of a set of forecasts - like an investment manager, or an economic policy-maker - looks for some judgement about possibilities to which history may not be a good guide. What if the underlying structure of the economy is changing - i.e. the model parameters are shifting?
Suppose, for example, the responsiveness of inflation to exchange rate changes is less than it used to be? What if the economy is more responsive than it used to be to recent changes in interest rates? For that matter, what if it is less responsive?