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provide.data(lcancer)
cases <- cbind(Easting/10000, Northing/10000)[Cancer == 1,]
controls <- cbind(Easting/10000, Northing/10000)[Cancer == 2,]
xlim <- range(Easting/10000)
ylim <- range(Northing/10000)
h <- c(0.05,0.05)
cases.sm <- sm.density(cases, h = h,
xlim = xlim, ylim = ylim, display = "none")
controls.sm <- sm.density(controls, h = h,
xlim = xlim, ylim = ylim, display = "none")
diff.obs <- sum((cases.sm$estimate -
controls.sm$estimate)^2)
cat("Observed value:",diff.obs, "\n")
nboot <- 20
p <- 0
ncase <- nrow(cases)
ncontrol <- nrow(controls)
for (i in 1:nboot) {
ind.control <- sample((1:ncontrol), ncontrol, replace=TRUE)
ind.case <- sample((1:ncontrol), ncase, replace=TRUE)
controls.star <- controls[ind.control,]
cases.star <- controls[ind.case,]
cases.sm.star <- sm.density(cases.star, h = h,
xlim=xlim, ylim = ylim, display = "none")
controls.sm.star <- sm.density(controls.star, h = h,
xlim=xlim, ylim = ylim, display = "none")
diff.star <- sum((cases.sm.star$estimate -
controls.sm.star$estimate)^2)
if (diff.star > diff.obs) p <- p + 1
cat(i, " ")
}
p <- p/nboot
cat("\np-value = ", p, "\n")
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