I'm trying to help several of our scientists with constructing inverse 
prediction intervals for models estimated with nonlinear least squares. So 
for example, we might estimate mean of y from a 4 parameter logistic 
function of x [e.g., using SSfpl in nls()], but then want to estimate a 
prediction interval for x estimated from y (calibration problem, inverse 
prediction).  I've done some searching of R archives and found the 
nlscal() function in package quantchem but this only seems to provide 
inverse estimates not intervals (although quantchem does have a function 
for inverse prediction intervals of linear models).  Is anyone aware of 
another function or package in R that will provide for inverse prediciton 
intervals for nonlinear least squares?  I will confess that I'm not 
cognizant of whether there is well developed, accessible theory for 
inverse prediction intervals in the nonlinear model.

Brian
 
Brian S. Cade

U. S. Geological Survey
Fort Collins Science Center
2150 Centre Ave., Bldg. C
Fort Collins, CO  80526-8818

email:  brian_cade@usgs.gov
tel:  970 226-9326
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