segmented (version 0.2-5)

slope: Slope estimates from segmented relationships

Description

Computes slopes of each `segmented' relationship in the fitted model.

Usage

slope(ogg, parm, conf.level = 0.95, rev.sgn=FALSE)

Arguments

ogg

an object of class "segmented", returned by any segmented method.

parm

the segmented variable whose slopes have to be computed. If missing all the segmented variables are considered.

conf.level

the confidence level required.

rev.sgn

vector of logicals. The length should be equal to the length of parm, but it is recycled otherwise. when TRUE it is assumed that the current parm is `minus' the actual segmented variable, therefore the sign i

Value

• slope returns a list of matrices. Each matrix represents a segmented relationship and its number of rows equal to the number of segments, while five columns summarize the results.

Details

To fit broken-line relationships, segmented uses a parameterization whose coefficients are not the slopes. Therefore given an object "segmented", slope computes point estimates, standard errors, t-values and confidence intervals of the slopes of each segmented relationship in the fitted model.

References

Muggeo, V.M.R. (2003) Estimating regression models with unknown break-points. Statistics in Medicine 22, 3055--3071.

See Also

See also davies.test to test for a nonzero differece-in-slope parameter.

Examples

set.seed(16)
x<-1:100
y<-2+1.5*pmax(x-35,0)-1.5*pmax(x-70,0)+rnorm(100,0,3)
out<-glm(y~1)
out.seg<-segmented(out,seg.Z=~x,psi=list(x=c(20,80)))
## the slopes of the three segments....
slope(out.seg)
rm(x,y,out,out.seg)