### Name: lines.survfit
### Title: Add Lines or Points to a Survival Plot
### Aliases: lines.survfit points.survfit
### Keywords: survival

### ** Examples

fit <- survfit(Surv(time, status) ~ sex, pbc,subset=1:312)
plot(fit, mark.time=FALSE, xscale=365.25,
        xlab='Years', ylab='Survival')
lines(fit[1], lwd=2, xscale=365.24)    #darken the first curve and add marks

# Add expected survival curves for the two groups,
#   based on the US census data
# The data set does not have entry date, use the midpoint of the study
efit <- survexp(~ ratetable(sex=sex,age=age*365.35,year=as.Date('1979/1/1')) +
            sex, data=pbc,  times=(0:24)*182)
temp <- lines(efit, lty=2, xscale=365.24, lwd=2:1)
text(temp, c("Male", "Female"), adj= -.1) #labels just past the ends
title(main="Primary Biliary Cirrhosis, Observed and Expected")