Not all conversion rates are created equal. A 57% rate from 33 leads is not the same as 36% from 706. Ivan Baldin reflects on how to add confidence interval bounds to your sales conversion charts using standard deviation and Excel stock chart candlesticks.

The standard ±1.645 SD approach to binomial distribution confidence intervals breaks down with small samples or extreme proportions. The Wilson score interval, proposed in 1927, handles both cases gracefully. This post walks through a practical call center QA example with formulas and a ready-made calculator.

Two employees, same average rating — but should we trust 10 scattered scores the same as 4 consistent ones? Inspired by Evan Miller’s work on ranking items with star ratings, this post walks through a Bayesian approach that accounts for both spread and sample size.