[R] Issue with 95% CI using MASS{confint}
Jennifer Sweatman
jenn.sweatman21 at gmail.com
Wed May 27 22:08:58 CEST 2015
I am trying to run a nonlinear model looking at seasonal abundance of
plants with the following limitations:
fit.nls.s<-nls(S_a~beta+m*time+alpha*sin(w*time+phi),
data= xy,
start=list(beta=2.1, m=0, alpha=2, phi = 1, w = 1),
upper=list(beta="inf", m="inf", alpha="inf", phi = 2*pi, w =
"inf"),
lower=list(beta="-inf", m="-inf", alpha=0, phi = 0, w =
0.0000001),
algorithm="port")
I want to know the 95% confidence intervals for all of my model
parameters. I have been using confint from the MASS package but I’m
getting some NA values. See output below:
confint(fit.nls.s)
2.5% 97.5%
beta 1.68170858 2.5635734
m 0.02810172 0.0710163
alpha NA 0.6755750
phi NA NA
w NA 1.0275199
The parameters I most need 95% CIs for are alpha and w (when alpha is
significant), but I consistently get NA for the lower limit of both. I
have changed my Upper/Lower limits for alpha, phi, and w to +/- infinity,
but my CIs still don’t include complete intervals. Any suggestions as to
what is going on here?
Thank you for your time
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