Confidence Interval

A range of values that remain plausible for an estimate under the method used.

Visual intuition

8 plausible

estimate

16 plausible

The interval is the plausible zone around an estimate

The pin is the estimate; the spotlight shows the range still plausible under the method.

Example

An estimate of 12 with a 95% interval from 8 to 16 is more precise than one from 2 to 22.

How It Works

A confidence interval is about estimation and uncertainty. Wider intervals less precision; narrower intervals mean more precision under the assumptions of the method.

Concepts

Confidence Intervals

A confidence interval is a range produced by a method that captures the true value a stated share of the time across repeated samples. It describes uncertainty in the estimating method, not a personal guarantee that one already-computed interval contains the truth.

Lessons

Point estimates shown with horizontal uncertainty ranges.

Uncertainty Needs Ranges

A measured number is usually a best estimate with sampling wobble around it, so honest comparisons need ranges as well as point estimates.

Related Facts

Data Tricks

4 min · medium

Several interval bars around a target line, with most bars crossing the target and one missing it.

A 95% confidence interval is not a 95% promise

A 95% confidence interval means the method works 95% of the time in repeated samples, not that this exact range now has a 95% chance of holding the truth.

Data Tricks

5 min · medium

A horizontal range bar with a center dot on the left, and a dashed threshold line with a marker crossing it on the right.

P-value vs confidence interval: what each one tells you

A p-value asks whether the data look surprising under a null model. A confidence interval asks which effect sizes remain plausible.