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st: RE: RE: RE: LevenbergMarquardt/summary


From   Miller.DavidJ@epamail.epa.gov
To   statalist@hsphsun2.harvard.edu
Subject   st: RE: RE: RE: LevenbergMarquardt/summary
Date   Tue, 09 Mar 2004 09:17:12 -0500



Dear Statalisters:

For those that might be interested, deconvolution  is a problem that is
also faced in risk assessment for pesticides.  We typically receive
composite data (typically 5 lbs)  on pesticide residues in fruits and
vegetables and need to assess acute risks that would be associated with
consuming single items.  We covered this topic in a Scientific Advisory
Panel meeting a couple of years ago.  Briefly (quoting our report):

"The challenge to OPP [U.S. Environmental Protection Agency's Office of
Pesticide Programs] has been to extrapolate from [United States
Department of Agriculture's] PDP composite data to provide single unit
values for use in acute risk assessments. In statistical terms, given
composite samples collected by the USDA, OPP is faced with the challenge
of estimating the parameters that describe the original population of
residue concentrations in servings of fruits or vegetables.
Specifically, the problem is to estimate the population mean  and the
population variance (sigma 2) from a set of composite samples where only
the composite sample mean (x_bar), the composite sample variance (s2),
and the number of units in each composite is known. With the estimation
of the population parameters ( and sigma 2 ) and assuming that the
distribution of residues in fruits and vegetables follows a lognormal
distribution (as established in previous goodness-of-fit studies), the
function that describes chemical residues on fruits/vegetables is
adequately established and ready for application into one of the
components of the Monte-Carlo model for the acute risk assessment."

 we looked at three different methods for deconvolution (MaxLIP, for
Maximum Likelihood Imputation seems the closest to what is being
discussed here). The report is available at:

http://www.epa.gov/scipoly/sap/2000/february/decompfin1woapp.pdf


The Scientific Advisory Panel response and recommendations is available
at:


http://www.epa.gov/scipoly/sap/2000/february/partialfinalreport06292000.pdf


Had I known about -denormix- then, I would have liked to have tried it
out.

David Miller
Office of Pesticide Programs
U.S. Environmental Protection Agency
703-305-5352 (voice)
703 605-1289 (fax)
OPP/Health Effects Division


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