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2012 Sep 19
0
Discrepancies in weighted nonlinear least squares
...DNase1)
This is the unweighted fit, in the code of 'nls' one can see that 'nls'
generates a vector wts <- rep(1, n).
Now for a weighted fit:
fm2DNase1 <- nls(density ~ SSlogis(log(conc), Asym, xmid, scal), DNase1,
weights = rep(1:8, each = 2))
in which I assign dcreasing weights for each of the 8 concentrations with 2
replicates.
Now with 'deviance' I get:
> deviance(fm1DNase1)
[1] 0.004789569
> deviance(fm2DNase1)
[1] 0.0164259
Telling me that the weighted fit has a significantly higher deviance (is a
worse fit).
Now with AIC (or BIC...