On Wed, 11 Nov 2015, Sven Schreiber wrote:
here's a little detail thingy about the built-in NBER recession
shading. It's
not really a bug (I think), but perhaps a little bit misleading.
Gretl uses the dates of the NBER peaks and troughs (I'm talking about monthly
data now) to determine the beginning and end of the shading. For example, one
NBER peak is 2001M3 (March), and so gretl's shading starts immediately after
February, covering all of the March interval in the plot. Therefore, the
observed March value of any plotted variable is a bit "later" (= to the
right), because the point is centered within the March interval. So the peak
value will always be "inside" the recession.
It seems that that's not the conventional way of presenting the recessions.
If you look at a time series plot on the FRED webpage for example, the March
value will be shown right at the beginning of the shading. Also, FRED offers
an indicator series for the NBER recessions which explicitly says "starting
with the period after the peak". It's a matter of convention, but I think the
FRED shading makes more sense than the current gretl shading.
So: I suggest that either the shading should start in the middle of the
period (middle of March in this example). But given that that may not be
feasible with gnuplot, I would suggest to adopt the FRED convention and start
the shading right after the peak dates.
Right now the documentation for a "plotbars" file says:
# Format: each non-comment line must contain two space-
# separated dates in the format YYYY:MM. These represent
# the start and end of "episodes" of some sort.
I take your point, but if we're to abide by this description, maybe
the appropriate fix would be to modify the example NBER file: make the
"start" of each NBER recession the month after the peak rather than
the peak itself. In this case no changes to the plotting code would be
required.
The alternative would be to leave the NBER file as it is and reword
the description, replacing "start" (of an episode) with something like
"period immediately preceding, as in NBER business cycle peaks". This
would have to be accompanied by a change to the plotting code.
Preferences/thoughts?
Allin