llprevr <- function(p, yes=c(0), no=c(0))
 {
 sumcheck <- sum(yes) + sum(no)
 if (sumcheck == 0) stop("Data must be entered for yes or no")
         if (sum(yes) == 0)  { llmck <-  sum(no) * log(1 - p)  }
           else { llmck <- sum(log(1 - (1 - p)^yes)) + sum(no) * log(1 - p)  }
         llmck
 }


dprev <- function(yes=c(0),no=c(0),disp='y',conf=.95)
{
	sumcheck <- sum(yes) + sum(no)
	if (sumcheck == 0) stop("Data must be entered for yes or no")
	if (sum(yes) == 0) 
	   {
		ucl <- 1 -exp(-qchisq(conf,1)/(2*sum(no)) )
		result <- c(0., 0., ucl)
	    if (disp == 'y') print("Lower 95% limit, MLE, Upper 95% limit = ")
	   result
	   }
	else if (sum(no) == 0)
	   {
		tfct <- function(p)
	      {
	       sum(log(1 - (1 - p)^yes)) + qchisq(conf,1)/2
	      }
     	   lcl <- uniroot(tfct, interval = c(0.0001, 1.))
	   result <- c(lcl$root, 1., 1.)
	   if (disp == 'y') print("Lower 95% limit, MLE, Upper 95% limit = ")
	   result
	   }
        else
          {
            #print(yes) ; #print(no)
	    llpmax <- optimize(llprevr, c(0., 1.), maximum = TRUE, yes = yes, no = no )
            #print(llpmax)
	    mval <- llprevr(llpmax$maximum,yes = yes, no = no)
	    tfct <- function(p)
	      {
		    llprevr(p, yes, no) - (mval - qchisq(conf,1)/2)
	      }
	    lcl <- uniroot(tfct, interval = c(0.00000001, llpmax$maximum))
	    ucl <- uniroot(tfct, interval = c(llpmax$maximum, 0.99999999))
	    result <- c(lcl$root, llpmax$maximum, ucl$root)
	    if (disp == 'y') print("Lower 95% limit, MLE, Upper 95% limit = ")
	    result
	    }
}