R/ci.R

In ldbounds: Lan-DeMets Method for Group Sequential Boundaries

"ci" <- function(conf,value,t,za,zb){
    zb[length(t)] <- value
    zcrit <- qnorm(1-(1-conf)/2)
    limit <- (value+c(-1,1)*zcrit)/sqrt(t[length(t)])
    target <- c(0,1)*conf+(1-conf)/2
    lim1 <- bisect(t,za,zb,target[1],limit[1],upper=TRUE)
    lim2 <- bisect(t,za,zb,target[2],limit[2],upper=TRUE)
    lim <- list(lower.limit=lim1,upper.limit=lim2)
    return(lim)
  }