Thats easy. Just create two levels for average income, smoothed over, say,
6 and 12 months (or whatever periods you choose, though be careful about
DT). Have an auxiliary for the difference between them and, depending on
whether the auxiliary is positive and negative, Bobs your uncle, as we say.
In practice, you might want to change the pesticide use if the auxiliary is
more than, say 10% of the smaller of the averages, so that you dont chase
Changing use next year is getting close to using a discrete formulation and
many people object to that. I dont because I want the model to do the same
things as the real system and for the same reasons, within the
simplification one has used.
Hope that helps. Give my regards to Yaman.
From: "Geoff Coyle" <Geoff.Coyle@btinternet.com>