Margin of error in polls, based on actual percentage and allowing for design effects

moe

moe = function(pct, N=1000, deff=c(1,2)){
	p.L = function(x, n) {
        ifelse (x == 0,0,qbeta(0.025, x, n - x + 1))
    }
    p.U = function(x, n) {
        ifelse(x == n,1,qbeta(0.975, x + 1, n - x))
    }
    N = rep(N,length(pct))
		
	lower = function(pct,deff){
		n = outer(N,deff,"/")
		x = n*pct/100
		round(100*p.L(x,n),1)
		}	
	upper = function(pct,deff){
		n = outer(N,deff,"/")
		x = n*pct/100
		round(100*p.U(x,n),1)
		}	
		
	l = lower(pct,deff)
	u = upper(pct,deff)	
	rval =list()	
	for (i in 1:length(deff)){	
	  rval[[i]] = cbind(l=l[,i],u=u[,i])
	  	rownames(rval[[i]])=pct
	
	}
	names(rval)=paste("Design.effect",deff,"=")
	rval
}