R/sigma2_hat_S1mS2.R

In EL2Surv: Empirical Likelihood (EL) for Comparing Two Survival Functions

sigma2_hat_S1mS2 <- function(t, fit, fit1, fit2) {
  n   <- fit$n
  out <- 1:length(t)*0
  for (i in 1:length(t)) {
    d1 <- fit1$n.event[fit1$time <= t[i] & fit1$n.event != 0]
    r1 <- fit1$n.risk [fit1$time <= t[i] & fit1$n.event != 0]
    d2 <- fit2$n.event[fit2$time <= t[i] & fit2$n.event != 0]
    r2 <- fit2$n.risk [fit2$time <= t[i] & fit2$n.event != 0]
    
    tcalc1 <- t[i] - fit1$time
    tcalc1[tcalc1 < 0] <- Inf
    which.min(tcalc1)
    
    tcalc2 <- t[i] - fit2$time
    tcalc2[tcalc2 < 0] <- Inf
    which.min(tcalc2)
    
    S1 <- fit1$surv[which.min(tcalc1)]
    S2 <- fit2$surv[which.min(tcalc2)]
    out[i] <- product(S1^2, sum(division00(d1, r1*(r1 - d1)))) + product(S2^2, sum(division00(d2, r2*(r2 - d2))))
  }
  return (out)
}