On 27/05/2015 4:08 PM, Jennifer Sweatman wrote: > 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?
Probably the profiling failed. You could look at plot(profile(fit.nls.s)) to see an indication of what's going on. If your tau values don't exceed 2 on one side of the estimate, you can't get a confidence limit on that side. Your data may not rule out any phi values, or may not rule out a lower limit on alpha or w. Duncan Murdoch ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.