About Probably Random

Probably Random is a reference site on statistics and probability for the people who use numbers at work but never trained as statisticians - analysts, marketers, product managers, researchers, journalists, and founders. If you run A/B tests, read studies, or build dashboards and keep bumping into terms like p-value, confidence interval, or regression to the mean, this is the place to look them up.

Every post covers exactly one concept and aims to be the definitive page on it: what it is, where it came from, the rules for using it, and the mistake people most often make. We anchor each idea in a plausible workplace scenario - an A/B test that looks like a winner, a hiring pipeline that seems biased, a sales dashboard that tells the wrong story - so the explanation lands where you'll actually use it. We name the common misreading out loud, because knowing the trap is half of avoiding it.

The maths appears only when it clarifies. If a formula makes something click, we show it and walk through the numbers. If it would just intimidate, we leave it out. The goal is understanding you can carry back to your own data, not a proof you have to trust on faith.

This is a reference, not a course and not a sales pitch. There's nothing to buy and no argument to win - just clear, citable explanations of the statistical ideas, tests, and pitfalls you run into on the job, written so you can read one entry, get what you came for, and get back to work.