// http://www.evanmiller.org/how-not-to-sort-by-average-rating.html
// http://gist.github.com/raw/63002/b53853727856bad494dcbb7ffed4fc17f289af92/gistfile1.rb

// $z is the pnormaldist with power = 0.05. I.e., pnormaldist(1-power/2)
function score($pos, $n) {
	if ($n == 0) { return 0; }
	$z = 1.95996397158435;
	$phat = 1.0*$pos/$n;
	return ($phat + $z*$z/(2*$n) - $z * sqrt(($phat*(1-$phat)+$z*$z/(4*$n))/$n))/(1+$z*$z/$n);
}