Confidence Interval

A confidence interval is a range of values that likely contains the true value of a metric, given the uncertainty in a sample-based estimate.

A "95% confidence interval" doesn't mean there's a 95% chance the true value falls in that specific range — technically, it means that if you repeated the same sampling process many times, 95% of the intervals constructed that way would contain the true value. It's a subtle distinction that gets misstated constantly, but it matters for correctly communicating uncertainty rather than false precision.

Wider confidence intervals mean more uncertainty, usually from a smaller sample size. A conversion rate reported as "3.2%" with no confidence interval is quietly hiding how much that number could reasonably vary — "3.2% (± 0.8%)" is a more honest, more useful statement.