options(na.action=na.exclude) # preserve missings
options(contrasts=c('contr.treatment', 'contr.poly')) #ensure constrast type

expect <- survexp(futime ~ 1,
                  rmap = list(age=(accept.dt - birth.dt), sex=1,
		year=accept.dt, race='white'), jasa, cohort=F, 

survdiff(Surv(jasa$futime, jasa$fustat) ~ offset(expect))
# Now fit the 6 models found in Kalbfleisch and Prentice, p139
sfit.1 <- coxph(Surv(start, stop, event)~ (age + surgery)*transplant,
				jasa1, method='breslow')
sfit.2 <- coxph(Surv(start, stop, event)~ year*transplant,
				jasa1, method='breslow')
sfit.3 <- coxph(Surv(start, stop, event)~ (age + year)*transplant,
				jasa1, method='breslow')
sfit.4 <- coxph(Surv(start, stop, event)~ (year +surgery) *transplant,
				jasa1, method='breslow')
sfit.5 <- coxph(Surv(start, stop, event)~ (age + surgery)*transplant + year ,
				jasa1, method='breslow')
sfit.6 <- coxph(Surv(start, stop, event)~ age*transplant + surgery + year,
				jasa1, method='breslow')


# Survival curve for an "average" subject,
#  done once as overall, once via individual method
surv1 <- survfit(sfit.1, newdata=list(age=-2, surgery=0, transplant=0))
newdata <- data.frame(start=c(0,50,100), stop=c(50,100, max(jasa1$stop)), 
                   event=c(1,1,1), age=rep(-2,3), surgery=rep(0,3),
                   transplant=rep(0,3), name=c("Smith", "Smith", "Smith"))
surv2 <- survfit(sfit.1, newdata, id=name)
# Have to use unclass to avoid [.survfit trying to pick curves,
#  remove the final element "call" because it won't match

# Survival curve for a subject of age 50, with prior surgery, tx at 6 months
#  Remember that 'age' in jasa 1 was centered at 48
data <- data.frame(start=c(0,183), stop=c(183,3*365), event=c(1,1),
		   age=c(2,2),  surgery=c(1,1), transplant=c(0,1), id=c(1,1))
summary(survfit(sfit.1, data, id=id))

# These should all give the same answer
# When there are offsets, the default curve is always for someone with
#  the mean offset.
j.age <- jasa$age -48
fit1 <- coxph(Surv(futime, fustat) ~ j.age, data=jasa)
fit2 <- coxph(Surv(futime, fustat) ~ j.age, jasa, init=fit1$coef, iter=0)
fit3 <- coxph(Surv(start, stop, event) ~ age, jasa1)
fit4 <- coxph(Surv(start, stop, event) ~ offset(age*fit1$coef), jasa1)

s1 <- survfit(fit1, list(j.age=fit3$means), censor=FALSE)
s2 <- survfit(fit2, list(j.age=fit3$means), censor=FALSE)
s3 <- survfit(fit3, censor=FALSE)
s4 <- survfit(fit4, censor=FALSE)

all.equal(s1$surv, s2$surv)
all.equal(s1$surv, s3$surv)
all.equal(s1$surv, s4$surv)

# Still the same answer, fit multiple strata at once
#  Strata 1 has independent coefs of strata 2, so putting in
#    the other data should not affect it
ll <- nrow(jasa1)
ss <- rep(0:1, c(ll,ll))
tdata <- with(jasa1, data.frame(start=rep(start,2), stop=rep(stop,2),
		    event=rep(event,2), ss=ss, age=rep(age,2),
		    age2 = (rep(age,2))^2 * ss))
fit <- coxph(Surv(start, stop, event) ~ age*strata(ss) + age2, tdata)
#  Above replaced these 2 lines, which kill Splus5 as of 8/98
#    Something with data frames, I expect.
#fit <- coxph(Surv(rep(start,2), rep(stop,2), rep(event,2)) ~
#			rep(age,2)*strata(ss) + I(rep(age,2)^2*ss) )
all.equal(fit$coef[1], fit3$coef)
s5 <- survfit(fit, data.frame(age=fit3$means, age2=0, ss=0), censor=FALSE)
all.equal(s5$surv[1:(s5$strata[1])],  s3$surv)

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survival documentation built on Feb. 16, 2023, 7:34 p.m.