nberDates returns a matrix with two columns of yyyymmdd dates
giving the Start and End dates of recessions fixed by the NBER.
nber.xy returns a list of x and y coordinates that can be fed
to polygon to draw NBER shadings on the current plot.
If the last row from nberDates() has a Start entry but no End
entry, the returned list will also include a vLine element that gives
the x coordinate of the last Start.
nberShade shades recession areas on the current plot. It calls
nber.xy to get x and y coordinates for the areas to be shaded
and then passes those coordinates along with its own arguments to
polygon to do the shading. It also draws a vertical
line at the appropriate location if the list returned by
nber.xy has a vLine element. romerLines draws vertical lines on the current plot at the
"Romer and Romer" dates when monetary policy is said to have become
contractionary.
nberShade(col = grey(0.8), border = FALSE, xpd = FALSE, ...)
nberDates()
nber.xy()
romerLines()FALSE) omits borders on the shaded
regions. TRUE draws borders in the foreground color.
Alternatively, specify a border color.polygonnber.xy returns a list. The other
functions described do not return anything useful.National Bureau of Economic Research. http://www.nber.org.
polygon