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noserver
2005 Jan 27
3
weighting in nls
...ing. I'm following the procedure outlined on p 244 of MASS (or at least I'm trying to).
Thus, I'm using mean data with heteroscedasticity so I'm weighting by n/ variance, where the variance is well known from a large data set. This weighting factor is available as the variable 'novervar'.
The function is a von Bertalanffy curve of the form weight~(a*(1-exp(-b*(age-c))))^3. Thus I'm entering the command in the form:
solb1wvb<-nls(~sqrt(novervar)*(weight-(a*(1-exp(-b*(age-c))))^3),data=solb1.na.rm,start=list(a=0.85,b=0.45,c=0.48))
Can anyone suggest what I'm doing...