I am looking for R code to be able to fit a linear-linear piecewise
model with person-specific changepoint. I have searched the web, but
have not been able to locate any code.
Below is my attempt at some code:
chgpt = function(a1,a2,a3,gam,wave){
yht=numeric(10)
y1=(wave <= gam)*(a1+(a2*wave))
y2=(wave > gam)*((a1+(a2-a3)*gam)+a3*wave)
yhat=y1+y2
return(yht)
}
nl.dat <- nlme(y ~ chgpt(a1,a2,a3,gam,wave)~wave|id,
data = ndat,
fixed = a1 + a2 + a3 + gam,
random = a1 + a2 + a3,
start = c(a1=10,a2=5,a3=1,gam=4.5))
summary(n1.dat)
I would appreciate any advice on this code or guidance as to where to
search for example code to fit this nonlinear mixed effects model.
Many thanks,
Jeff Harring
--
**********************************************************
Jeffrey R. Harring, Assistant Professor
Department of Measurement, Statistics & Evaluation (EDMS)
1230 Benjamin Building
University of Maryland
College Park, MD 20742-1115
Phone: 301.405.3630
Fax: 301.314.9245
Email: harr...@umd.edu
Web: http://www.education.umd.edu/EDMS/fac/Harring/webpage.html
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