Hi,<br><br>&nbsp; If you run a regression like Y= XB + GH + error where GH
is unobserved so the actual regression you will run is Y = XB + (GH +
error) and then use the output to forecast various things. If G has
variables in it that trend in one direction or another over time (
i.e population in a given area) then will the forecast get less
accurate as we get away from the time period used to estimate the
coefficients and if so, is there some test that can be used to give an
idea of how often the model should be re-estimated? This would also
mean that the R^2 should decrease as we get away from the time period
used for estimation right?
<br><br>Thanks,<br><span class="sg"><br>Chris</span>