[R] bootstrapped CI for nonlinear models using nlsBoot from nlstools

[Francisco Mora Ardila]

Hi all

I´m trying to get confidence intervals for parameters from nls modeling. I fitted a nls 
model to the following variables:

> x
 [1]   2   1   1   5   4   6  13  11  13 101 101 101
> y
 [1]  1.281055090  1.563609934  0.001570796  2.291579783  0.841891853
 [6]  6.553951324 14.243274230 14.519899320 15.066473610 21.728809880
[11] 18.553054450 23.722637370

The model fitted was:

model<-nls(y~SSgompertz(x,a,b,c))

and it worked OK, with the following results:

Formula: y ~ SSgompertz(x, a, b, c)

Parameters:
  Estimate Std. Error t value Pr(>|t|)    
a  21.2426     0.9689  21.924 4.03e-09 ***
b   5.3330     1.4722   3.622  0.00555 ** 
c   0.8045     0.0274  29.364 3.01e-10 ***

Then, trying to get confidence intervals for the parameters using the nlsBoot function 
in the nlstools package I got this error:

> modelboot<-nlsBoot(model)
Error en data2[, var1] <- fitted1 + sample(scale(resid1, scale = FALSE),  : 
  objeto de tipo 'environment' no es subconjunto

I´ve tried with another response variable and other self starting function (SSlogis) and 
got the same error.

Any suggestions?

Francisco


----------------------
Francisco Mora Ardila
Estudiante de Doctorado
Centro de Investigaciones en Ecosistemas
Universidad Nacional Autónoma de México