Calculating A/B Test Sample Size

optimizely.js

"use strict";

//based on https://www.optimizely.com/resources/sample-size-calculator/
function getSampleSize() {
    let effect = 0.05; // Minimum Detectable Effect
    let significance = 0.95; // Statistical Significance
    let conversion = 0.05; // Baseline Conversion Rate

    let c = conversion - (conversion * effect);
    let p = Math.abs(conversion * effect);
    let o = conversion * (1 - conversion) + c * (1 - c);
    let n = 2 * significance * o * Math.log(1 + Math.sqrt(o) / p) / (p * p);
    
    return Math.round(n);
}

qualtrics.js

"use strict";

//based on https://www.qualtrics.com/blog/determining-sample-size/
function getSampleSize() {
    let z = 1.96;//z-score for confidence level (95% for 1.95)
    let p = 0.5;//standard of deviation (0.5 for 50%/50%)
    let e = 0.05;//margin of error

    return (z * z) * p * (1 - p) / (e * e);
}