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Evan Miller source code for sample size from my blog post http://www.alfredo.motta.name/ab-testing-from-scratch/
function num_subjects(alpha, power_level, p, delta) {
var t_alpha2 = ppnd(1.0-alpha/2);
var t_beta = ppnd(power_level);
var sd1 = Math.sqrt(2 * p * (1.0 - p));
var sd2 = Math.sqrt(p * (1.0 - p) + (p + delta) * (1.0 - p - delta));
return (t_alpha2 * sd1 + t_beta * sd2) * (t_alpha2 * sd1 + t_beta * sd2) / (delta * delta);
}
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