[R] supsmu vs. ppr

[david.beede@mail.doc.gov]

I used the supersmoother function in the modreg package as follows:

super <- supsmu(ilogemp,award)

Then I decided that I might want additional explanatory variables (other
than ilogemp) in my model.  The ppr function in modreg seemed a logical
extension of supsmu from univariate to multidimensional explanatory
variables.  As a "check" I ran the following:

pprest <- ppr(ilogemp,award,nterms=1),

figuring I'd get the same results.  I did not.  First, the fitted values
ppr output is not rescaled back to the original scale of award.
Eventually, I figured out that the ppr fitted values had mean zero and
variance=1, so I thought I needed to multiply ppr's fitted values by the
standard deviation of award (pprest$ys) and then add in the mean of award
(pprest$yb), but the result is still way off from the fitted values from
supsmu.

Does anyone have any thoughts about this?

Thanks,
David N. Beede
Economist
Office of Policy Development
Economics and Statistics Administration
U.S. Department of Commerce
Room 4858 HCHB
14th Street and Pennsylvania Avenue, N.W.
Washington, DC  20230
Voice:  202.482.1226
Fax:    202.482.0325
e-mail:  david.beede at mail.doc.gov

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