`ochiai` <-
function(x,y) 
{
  ai <- (y[y>0]-x[y>0])!=y[y>0]
  a <- length(ai[ai==TRUE])
  b<-length(x[x>0])-a
  c<-length(y[y>0])-a
  och<- sqrt((a/(a+b))*(a/(a+c)))
  return(och)
}