R/ci.median.R

In asbio: A Collection of Statistical Tools for Biologists

ci.median<-function(x,conf=.95){
n<-nrow(as.matrix(x))
if(qbinom((1-conf)/2,n,0.5)==0)stop("CI not calculable")
L<- qbinom((1-conf)/2,n,0.5)
U<-n-L+1
if(L>=U)stop("CI not calculable")
order.x<-sort(x)
res<-list()
res$head<-paste(paste(as.character(conf*100),"%",sep=""),c("Confidence interval for population median"))
res$ci<-c(median=median(x),lower=order.x[L],upper=order.x[n-L+1])
res$ends<-c("Estimate",paste(as.character(c((1-conf)/2,1-((1-conf)/2))*100),"%",sep=""))
res$coverage<-1-(2*pbinom(q=L-1,n,0.5))
class(res)<-"ci"
res
}