Weighted average: what it means
An average in which some values count for more than others, according to their size or importance.
A weighted average gives each value a weight that reflects how much it should count. A simple average of three hospitals' waiting times treats a small hospital and a large one equally; a weighted average counts each in proportion to how many patients it treats.
Worked example
Hypothetical area A has 10,000 people and a rate of 2%; area B has 90,000 people and a rate of 6%. The simple average of the two rates is 4%, but the weighted average, which is the actual rate for the combined population, is 5.6%.
Why it matters when checking a claim
- Averaging regional or local rates without weighting can give a national figure that does not match the real one.
- Price indices such as CPI are weighted averages of price changes, with weights based on household spending. See survey weighting.
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Related terms
- Mean: The total of all values divided by how many there are. Often what people mean by 'average', it can be pulled up or down by a few extreme values.
- Survey weighting: Adjusting survey responses so the sample matches the known make-up of the population, such as by age, sex and region.
- CPI (Consumer Prices Index): The UK's main measure of consumer price inflation for the Bank of England's 2% target. It tracks the prices of a basket of goods and services bought by households.
- Per capita (per head): A total divided by the number of people in the population, such as GDP per head or spending per person, to allow fair comparison between places or years.
More averages, rates and risk terms: Median · Mean · Per capita (per head) · Rate per 100,000 · Crude rate · Age-standardised rate · Odds, risk, relative and absolute risk · Deciles and quintiles.