I wish to compare several "products" in terms of their dose-response functions as estimated by smooths via the gam function. Included in the experimental evaluations are zero-dose ("blank") measurements. I want to set up the gam estimation so that the fitted smooths for the several products converge to a common value at zero dose equal to the estimated response for the blank. I've read Simon Wood's post of Mar 26, 2013; 7:28am providing an example of constraining a spline to pass through a particular point - but I don't want to specify the response value there, I want to estimate it. Can this be done with gam? If so, please point me to the relevant locations in the gam or mgcv documentation or in Simon Wood's book on how to do this, or if possible provide example R code. Thanks! -Bleary
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