@shotlingo/ab-test-sample-size

A/B test sample-size, total-size, and test-duration calculator for App Store Product Page Optimization and Google Play Store Listing Experiments. Two-proportion z-test (95% two-sided significance, 80% power). Zero dependencies, no network calls.

Full interactive reference (calculator + worked examples): shotlingo.com/tools/ab-test-sample-size-calculator

Install

npm install @shotlingo/ab-test-sample-size

Usage

import {
  sampleSizePerVariant,
  totalSampleSize,
  estimateTestDurationDays,
} from '@shotlingo/ab-test-sample-size';

// 25% baseline conversion rate, detect a 10% relative lift
sampleSizePerVariant(25, 10);
// => 4501

totalSampleSize(25, 10);
// => 9002

// With 200 visitors/day per variant, how many days to collect that sample?
estimateTestDurationDays(200, 25, 10);
// => 23

API

• sampleSizePerVariant(baselineRatePct: number, mdeRelativePct: number): number — required sample size per variant. Returns Infinity for degenerate inputs (non-improving or out-of-range rates) instead of NaN.
• totalSampleSize(baselineRatePct: number, mdeRelativePct: number): number — sample size across both variants.
• estimateTestDurationDays(dailyVisitorsPerVariant: number, baselineRatePct: number, mdeRelativePct: number): number — days to collect the required sample, floored at 7 (daily conversion swings by weekday, so shorter tests skew toward whichever days they happened to cover).
• Z_ALPHA_2_SIDED_95, Z_BETA_POWER_80 — the fixed z-values behind the defaults.

License

MIT