[R] significant difference between Gompertz hazard parameters?

[piltdownpunk]

Hello, all.

I have co-opted a number of functions that can be used to plot the
hazard/survival functions and associated density distribution for a Gompertz
mortality model, given known parameters.  The Gompertz hazard model has been
shown to fit relatively well to the human adult lifespan.  For example, if I
wanted to plot the hazard (i.e., mortality) functions:

pop1 <- function (t)
	{
		x=c(0.03286343, 0.04271132)
		a3<-x[1]
		b3<-x[2]
		shift<-15     # only considering mortality after 15 years
		
		h.t<-a3*exp(b3*(t-shift))
		return<-h.t
}

pop2 <- function (t)
	{
		x=c(0.02207778, 0.04580059)
		a3<-x[1]
		b3<-x[2]
		shift<-15     # only considering mortality after 15 years
		
		h.t<-a3*exp(b3*(t-shift))
		return<-h.t
}

ylab.name <- expression(paste(italic(h),"(",italic(a),")"))
plot(seq(15,80,1),pop1(seq(15,80,1)),type='l',ylab=ylab.name,xlab='Age
(years)',ylim=c(0,0.8))
lines(seq(15,80,1),pop2(seq(15,80,1)),lty=2)

How may I test for a significant difference in the hazard parameters that
define the mortality experience for these two populations?  Thanks in
advance.

Regards,
Trey

-----
Trey Batey---Anthropology Instructor
Division of Social Sciences
Mt. Hood Community College
Gresham, OR  97030
Alt. Email:  trey.batey[at]mhcc[dot]edu
--
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