Factcheck LedgerReceipts, not verdicts
Request a check
Menu
Fact checks
Economy and money
Public services
Parliament and politics
Where you live
UK and the world
Data and tools

How we workEmail alertsRequest a check

Confidence interval: what it means

A range around an estimate that shows how much it could vary because it comes from a sample. A 95% interval is the usual standard.

A confidence interval is a range around an estimate that reflects sampling uncertainty. A 95% confidence interval means that if the survey were repeated many times with fresh random samples, about 95% of the intervals calculated would contain the actual population value.

Worked example

A hypothetical survey estimates unemployment at 1,500,000 with a 95% confidence interval of plus or minus 80,000, so the range is 1,420,000 to 1,580,000. If the next estimate is 1,530,000, the change of 30,000 is well inside that range and may simply reflect sampling.

How it trips up claims

  • Two estimates whose intervals overlap may not be meaningfully different. A formal test of statistical significance on the change is the better check.
  • Smaller groups have wider intervals, so regional or subgroup rankings are often less certain than they appear.
  • Confidence intervals cover sampling error only. They do not capture non-response bias or measurement problems.

ONS bulletins and the Crime Survey for England and Wales note when changes are statistically significant.

Also searched as: margin of error, 95% confidence interval, CI, sampling variability

Official definitions: ONS: Uncertainty and how we measure it · ONS: Labour Force Survey user guidance

Key figures where it matters

Questions that use this term

Related terms

  • Statistical significance: A test of whether a difference between estimates is larger than would be expected from sampling variation alone. It does not mean the difference is large or important.
  • Survey sample: The group of people or businesses selected to take part in a survey, chosen so that their answers can be used to estimate figures for the whole population.
  • Response rate: The share of people or businesses selected for a survey who actually take part. Lower response rates can make estimates less precise and risk bias.

More statistics, surveys and quality terms: Accredited official statistics · Official statistics in development · Pre-release access · Survey sample · Response rate · Administrative data · Provisional figures · Revisions · Statistical significance · Headline figure · Sample size · Labour Force Survey (LFS).