A radio host saw 4 listener texts for and 4 against, and called the audience evenly split. The math says otherwise: on a sample of 8, the true share is anywhere from 21% to 79%. Here’s how to compute that – and why you’d need 271 texts.

A voice robot beats call center with 8% vs. 6% promo code activations. But how many calls do you actually need to prove the difference is real? We walk through the A/B test math and find the minimum sample size for 95% confidence using Goal Seek in Google Spreadsheets, Z-score and SD.

A contractor claims every fifth call has a bad connection. How many good calls in a row do you need to disprove him? This post uses a binomial hypothesis test to calculate the exact sample size for 99% confidence — with the Google Sheets formula included.