Glossary · Phase 2 · Math, when you need it
Confidence interval
A range that probably contains the true value, given the data you sampled.
A map app doesn't promise you'll arrive at exactly 6:14. It says "6:10 to 6:20". A range is more honest than one exact number. A confidence interval does the same for an estimate.
Try it now
Each run is 1,000 experiments. Each one measures the conversion rate from n visitors. Raise the visitors per experiment and watch the spread of measured rates shrink.
Learn it properly
Samples and confidence · Estimate from a sample and say how sure you are. About 30 minutes.
Other terms from the same lesson
- bootstrap: Estimating uncertainty by resampling your own data, with replacement, many times and seeing how much the answer moves.
- margin of error: The plus-or-minus around an estimate, such as 3.2% ± 0.8%. It is usually about two standard errors.
- resample: Draw a new sample from your data, picking rows at random with replacement, to mimic collecting fresh data.
- standard error: How much an estimate from a sample would wobble if you took a fresh sample. Bigger samples give smaller standard errors.
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