Wilson score formula with range

wilson-score-range.js

/**
 * Wilson score formula with range
 *
 * @param {number} sum Objects sum
 * @param {number} total Total objects
 * @param {object} range Objects (votes) range: [0, 1] or [0, n]
 * @param {number} z Confidence level
 */
function wilsonScoreRange(sum, total, range, z) {
    // http://amix.dk/blog/post/19588

    if (total <= 0 || total < sum) return 0;
    // z:
    // 95% = 1.644853
    // 99% = 2.326348
    z = (typeof z == 'number' ? z : 1.644853);
    range = (typeof range == 'object' ? range : [0, 1]);

    var min   = range[0],
        width = ( range[1] - min ).toFixed(10),
        phat  = (sum - total * min) / width / total.toFixed(10),
        rating = (phat + z*z / (2*total) - z*Math.sqrt( (phat * (1-phat) + z*z / (4*total) ) / total) ) / (1 + z*z / total);

    return rating * width + min;
}