[R] Breakpoints for multiple variables using Segmented

[Matthew Betts]

Hi all,

I am using the package “Segmented” to estimate logistic regression models
with unknown breakpoints (see Muggeo 2003 Statistics in Medicine
22:3055-3071). In the documentation it suggests that it might be possible to
include several variables with breakpoints in the same model: “Z = a vector
or a matrix meaning the (continuous) explanatory variable(s) having
segmented relationships with the response”. However, the syntax for
including multiple “Z” and “psi” (“starting values for the break-point(s)”)
is not stated. Does anyone have any suggestions?

Here is an example of correct code for detecting single breakpoint:

model.seg<-segmented.glm(obj = model.glm, Z = predictor_variable, psi = 2 ,
it.max = 50)

Thanks very much for your help.


Matthew G. Betts, Ph.D.
NB Cooperative Fish and Wildlife Research Unit
Faculty of Forestry and Environmental Management
University of New Brunswick 
UNB Tweedale Centre
Hugh John Flemming Forestry Complex
1350 Regent St., Fredericton, N.B.
E3C 2G6
(506) 447-3408
http://www.unb.ca/web/acwern/people/mbetts/mbetts.htm