dear Peter,
Currently segmented handles multiple breakpoints for several variables
(the limit discussed in the msg 2006 has been fixed..).
However you are looking for a somewhat complicated model where the
breakpoint of the relationship 's.size' and 'R.AUC' depends on another
covariate 'bedekking'. Namely it is an interaction in the breakpoint
parameter (rather then in a linear parameter).
Currently segmented is not able to deal with these interactions, and
splitting up the data into two or three groups according the values of
bedekking could be a feasible alternative.
Hope this helps you,
vito
Il 01/06/2012 11.35, Peter Hoitinga ha scritto:
Hello,
I'm attempting to find multiple breakpoints in an association of my
response variable (R.AUC) with two explanatory variables ('s.size' and
'bedekking'). The association between 's.size' and 'R.AUC' shows a
plateau, but the value when this plateau is reached is differs for
different values of 'bedekking'.
Initially I thought these different values could be assessed by the
'segmented' function in the package of the same name, but this only
seems to give one value of a breakpoint for each explanatory variable.
A similar issue was treated in the following message from 2006:
https://stat.ethz.ch/pipermail/r-help/2006-January/086446.html
Does anybody know whether there are any packages that do have a
function for this? Or might it be a possibility to split up the data
per value of 'bedekking' and then do the segmented function?
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--
====================================
Vito M.R. Muggeo
Dip.to Sc Statist e Matem `Vianelli'
Università di Palermo
viale delle Scienze, edificio 13
90128 Palermo - ITALY
tel: 091 23895240
fax: 091 485726
http://dssm.unipa.it/vmuggeo
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