Glossary of statistics terms

Plain-English definitions of the terms that official figures use, with a worked example of each and the ways each one is commonly misread.

Measuring change over time

Terms for comparing one period with another: real and cash terms, percentage points, index numbers, seasonal adjustment and growth rates.

• Real terms
  A figure adjusted to remove the effect of inflation, so amounts from different years can be compared by what they would buy rather than their face value.
• Cash terms
  A money figure stated at the prices of the time it refers to, with no adjustment for inflation. Also called nominal terms.
• Percentage point
  The arithmetic difference between two percentages. A rise from 4% to 5% is one percentage point, but a 25% increase in the rate.
• Year-on-year change
  The change between a figure for one period and the same period twelve months earlier, such as March this year compared with March last year.
• Quarter-on-quarter change
  The change from one three-month period to the next, such as April to June compared with January to March. Used for GDP growth.
• Rolling average
  An average recalculated each period over a fixed window, such as the latest three months or twelve months, to smooth out short-term ups and downs.
• Index number
  A number that shows how a value compares with a chosen reference period set to 100. An index of 110 means 10% higher than the reference period.
• Base year
  The reference period against which an index is set to 100, or whose prices are used to express real-terms figures.
• Seasonally adjusted
  Figures that have had regular calendar patterns removed, such as Christmas shopping or summer jobs, so that underlying movements between months or quarters can be seen.
• Base effect
  When a rate of change is pushed up or down by what happened in the comparison period, rather than by what is happening now.
• Compound annual growth rate
  The constant yearly growth rate that would take a figure from its starting value to its end value over a period. Different from simply dividing total growth by the number of years.
• Discontinuity (break in series)
  A point where the way a statistic is collected or defined changes, so figures before and after it cannot be compared directly.

Averages, rates and risk

How averages and rates are calculated, and why the choice of median, mean, per-head or age-standardised figures changes what a number says.

• Median
  The middle value when all values are ordered from lowest to highest. Half are above and half below, so a few very large values cannot pull it up.
• 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.
• 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.
• Rate per 100,000
  The number of events divided by the population and multiplied by 100,000, so areas of different sizes can be compared on a like-for-like basis.
• Crude rate
  A rate calculated by dividing events by the whole population, with no adjustment for differences in age structure between places or over time.
• Age-standardised rate
  A rate adjusted to a standard population age structure, so that places or years with older or younger populations can be compared fairly.
• Odds, risk, relative and absolute risk
  Risk is the chance an event happens out of everyone exposed; odds compare those it happens to with those it does not. Relative risk compares two groups' risks.
• Deciles and quintiles
  Ways of dividing a ranked population into equal groups: ten groups (deciles) or five groups (quintiles), often used for income.
• Weighted average
  An average in which some values count for more than others, according to their size or importance.

Inflation, prices and the economy

The price indices, GDP measures and Bank of England tools that sit behind most economic claims.

• 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.
• CPIH
  The Consumer Prices Index including owner occupiers' housing costs. The ONS's lead measure of consumer price inflation, it adds housing costs and council tax to CPI.
• RPI (Retail Prices Index)
  An older UK price index still used in some contracts, index-linked gilts and student loans. It is not an accredited official statistic and usually runs above CPI.
• Core inflation
  Inflation measured without the most volatile items, usually energy, food, alcohol and tobacco, to show underlying price pressure.
• Nominal GDP
  Gross domestic product measured at current prices, without adjusting for inflation. Used for debt-to-GDP and spending-to-GDP ratios.
• Chained volume measure
  The ONS method for showing GDP and other output after removing price changes, by linking year-to-year volume changes together. This is 'real' GDP.
• Purchasing power parity (PPP)
  A conversion rate that reflects how much the same basket of goods costs in different countries, used to compare living standards and economy size internationally.
• Bank Rate
  The interest rate the Bank of England pays on reserves held by commercial banks. Set by the Monetary Policy Committee, it is often called the base rate.
• Quantitative easing (QE)
  The Bank of England's purchase of assets, mainly government bonds, with newly created central bank money to lower longer-term interest rates and support spending.
• Quantitative tightening (QT)
  The Bank of England reducing the stock of government bonds it bought under quantitative easing, by letting them mature and by selling them.
• GDP deflator
  A measure of price change across the whole economy, used by HM Treasury to convert public spending figures from cash terms into real terms.
• Output gap
  The difference between what the economy is actually producing and an estimate of what it could produce sustainably. It cannot be measured directly.
• Productivity
  How much output the economy produces for each unit of input. The ONS headline measure is output per hour worked.
• Technical recession
  Two consecutive quarters of falling real GDP. A widely used rule of thumb rather than a legal or official definition.
• Current account (balance of payments)
  The UK's net position on trade in goods and services, plus income flows such as investment earnings and transfers with the rest of the world.
• Balance of trade
  The value of a country's exports minus its imports. A negative balance is a trade deficit.
• Monetary Policy Committee (MPC)
  The nine-member Bank of England committee that sets Bank Rate and decides on gilt purchases and sales to meet the government's inflation target.
• Gross value added (GVA)
  The value of goods and services produced, minus the cost of the inputs used to make them. GDP is GVA plus taxes on products, minus subsidies.

Jobs, pay and living standards

How official statistics count people in work, out of work and on low incomes, and the definitions that make the counts differ.

• ILO unemployment
  The internationally agreed definition of unemployment: people without a job who have looked for work in the past four weeks and can start within two weeks.
• Claimant count
  The number of people claiming benefits principally because they are unemployed: Jobseeker's Allowance and Universal Credit claimants required to look for work.
• Economic inactivity
  People who are not in work and not looking for or available for work, such as students, carers, retired people and those who are long-term sick.
• Full-time equivalent (FTE) and headcount
  FTE converts part-time posts into full-time units, so two half-time staff count as one FTE. Headcount counts each person once regardless of hours.
• Headcount
  A count of individual people, each counted once regardless of how many hours they work or how many posts they hold.
• Relative and absolute poverty
  Relative poverty means household income below 60% of the median in that year. Absolute poverty uses 60% of a fixed past median, adjusted only for inflation.
• Before and after housing costs (BHC and AHC)
  Two ways of measuring household income: before housing costs (BHC) counts income as received; after housing costs (AHC) deducts rent, mortgage interest and similar costs.
• NEET (not in education, employment or training)
  Young people, usually aged 16 to 24, who are not in any form of education, employment or training. Counts include both unemployed and economically inactive young people.
• Employment rate
  The percentage of people in a given age group who are in work. The UK headline rate covers people aged 16 to 64.
• Average weekly earnings (AWE)
  The ONS monthly measure of what employees in Great Britain are paid each week on average, reported for regular pay and total pay including bonuses.
• Payrolled employees (PAYE RTI)
  The count of employees paid through HMRC's PAYE system, published monthly from Real Time Information. It covers employees only, not the self-employed.
• Real household disposable income (RHDI)
  The total income households have available to spend or save after taxes and benefits, adjusted for inflation. Often expressed per head.
• Households below average income (HBAI)
  The DWP's annual statistics on the distribution of household income in the UK, the main source for official poverty figures.
• Gini coefficient
  A single number summarising inequality of income or wealth, from 0 (everyone has the same) to 100 or 1 (one person has everything).

Public finances

Debt, borrowing, fiscal rules, gilts and the language of forecasts and outturns used by HM Treasury, the ONS and the OBR.

• Public sector net debt (PSND)
  The public sector's financial liabilities, mainly government bonds, minus its liquid assets such as cash. The headline measure of the national debt.
• Public sector net borrowing (PSNB)
  The gap between what the public sector spends and what it receives in a period. Often called the deficit; it adds to debt.
• Fiscal rules
  Targets the government sets for itself on borrowing and debt, written into the Charter for Budget Responsibility and assessed by the Office for Budget Responsibility.
• Gilts
  Bonds issued by the UK government to borrow money. They pay a fixed interest (coupon) and repay the face value at maturity; index-linked gilts rise with RPI.
• Outturn
  The actual recorded figure for a period that has ended, as opposed to a plan, budget or forecast for it.
• Forecast and projection
  A forecast is a best estimate of what will happen. A projection shows what would happen if stated assumptions hold, without claiming they will.
• Fiscal headroom
  The margin by which the government is forecast to meet its main fiscal rule. It is a forecast, not money in a bank account, and it changes every time the OBR updates its numbers.
• Structural deficit
  The part of government borrowing that would remain even if the economy were running at its normal capacity. Also called the cyclically adjusted deficit.
• Current budget
  Government day-to-day receipts minus day-to-day spending, leaving out investment. A current budget surplus means taxes cover running costs.
• Debt interest
  What the government pays each year to service its debt, including interest on gilts and the uplift on index-linked gilts when inflation rises.
• Public sector net financial liabilities (PSNFL)
  A wider measure of public sector debt that subtracts all financial assets, such as student loans and equity holdings, not just cash and reserves.
• Spending review
  The process in which HM Treasury sets government departments' budgets for several years ahead, usually covering day-to-day and capital spending.
• Departmental expenditure limits (DEL) and annually managed expenditure (AME)
  The two halves of UK public spending: DEL is the budget each department is given, AME is spending such as pensions and benefits that depends on demand.
• Tax burden
  Total tax receipts as a share of GDP. Used to compare the overall level of tax over time or between countries, rather than the tax paid by any one household.
• Fiscal drag
  The rise in tax paid when tax thresholds are frozen or rise more slowly than incomes, pulling more income and more people into tax or into higher bands.
• Barnett formula
  The mechanism HM Treasury uses to change the block grants for Scotland, Wales and Northern Ireland when spending on comparable services in England changes.

Statistics, surveys and quality

The status labels, data sources and quality measures that tell you how much weight a published figure can bear.

• Accredited official statistics
  Official statistics that the Office for Statistics Regulation has independently reviewed and confirmed meet the highest standards of the Code of Practice for Statistics.
• Official statistics in development
  New or substantially changed official statistics that are still being tested and developed, and published early so users can give feedback. Formerly 'experimental statistics'.
• Pre-release access
  Limited access to official statistics given to named officials and ministers shortly before publication, under rules set by law, so they can prepare responses.
• 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.
• Administrative data
  Information collected by organisations while running a service, such as tax records, benefit claims or hospital activity, and then used to produce statistics.
• Provisional figures
  Early estimates published before all data are in, so users get timely figures. They are expected to be updated when later data arrive.
• Revisions
  Changes to previously published figures, made when more complete data, improved methods or updated seasonal factors become available. A normal part of official statistics.
• Confidence interval
  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.
• 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.
• Headline figure
  The main summary number that a statistical release leads with, such as annual CPI inflation or quarterly GDP growth. Other measures in the same release can tell a different story.
• Sample size
  The number of people, households or businesses that took part in a survey. Larger samples give more precise estimates, but size alone does not remove bias.
• Labour Force Survey (LFS)
  The ONS household survey behind the UK's headline employment, unemployment and inactivity figures.
• Correlation and causation
  Two things moving together (correlation) does not show that one causes the other (causation). Other factors, chance or reverse causation can explain the pattern.
• Selection bias
  A distortion that arises when the people or cases included in data differ systematically from the population a claim is about.
• Survey weighting
  Adjusting survey responses so the sample matches the known make-up of the population, such as by age, sex and region.
• Outlier
  A value that is unusually far from the rest of the data. It may be a genuine extreme or an error, and it can distort averages and trends.
• Data suppression
  Withholding or rounding small numbers in published tables so that individuals cannot be identified, or because estimates are too unreliable to publish.
• Census
  A count of every person and household in a country on a set day, usually held every ten years. The UK census is run separately in each nation.

Health and population

Terms used in NHS, mortality and migration statistics, from incidence and prevalence to referral to treatment.

• Incidence and prevalence
  Incidence counts new cases arising in a period. Prevalence counts everyone who has the condition at a point or over a period, whether new or existing.
• Cohort
  A group of people who share a starting point, such as being born in the same year or starting school together, followed over time.
• Net migration
  Long-term immigration minus long-term emigration over a period, usually a rolling year. It measures the net change in population from migration.
• Referral to treatment (RTT)
  The waiting time measure for planned hospital care in England: the time from referral to the start of consultant-led treatment. The NHS standard is 18 weeks.
• Elective care
  Planned, non-emergency hospital treatment such as hip replacements, cataract operations and many outpatient appointments, usually after a referral.
• Four-hour A&E standard
  The NHS standard that patients should be admitted, transferred or discharged within four hours of arriving at A&E. The constitutional standard is 95%.
• Ambulance response categories
  The four categories that ambulance calls in England are sorted into by urgency, each with its own response time standard.
• Waiting list pathways
  The unit the NHS in England uses to count its waiting list. One patient waiting for two different treatments counts as two pathways.
• No criteria to reside
  Hospital patients in England who are medically ready to leave but are still in a bed, often because care or support outside hospital is not yet arranged.
• Healthy life expectancy
  The average number of years a person can expect to live in good health, based on current death rates and people's own rating of their health.
• Asylum backlog
  The number of asylum claims awaiting a decision. Usually means claims awaiting an initial Home Office decision, not appeals.
• Asylum grant rate
  The share of asylum decisions in a period that resulted in a grant of protection or other leave, usually calculated at the initial decision stage.
• Irregular migration (illegal entry routes)
  People arriving in the UK without permission, such as by small boat or hidden in vehicles. Home Office statistics now use the term illegal entry routes.
• Refugee status
  Protection granted to someone who has shown a well-founded fear of persecution in their own country under the 1951 Refugee Convention.
• Mid-year population estimates
  The official annual estimates of how many people live in the UK and each area on 30 June, used as denominators for most per-head figures.
• Dependency ratio
  The number of people of pension age, or of children and pensioners, compared with the number of people of working age.

Geography and time periods

Which countries and which twelve months a figure covers: UK or Great Britain, England and Wales, financial or calendar year.

• Great Britain and the United Kingdom
  Great Britain is England, Scotland and Wales. The United Kingdom is Great Britain plus Northern Ireland. Some statistics cover only one or the other.
• England and Wales
  A single legal jurisdiction, so crime, courts, prisons and death registration statistics are often published for England and Wales together.
• Financial year
  The UK government's accounting year, running from 1 April to 31 March. Written as 2025-26 or FYE March 2026. The tax year runs 6 April to 5 April.
• Calendar year
  January to December. Used for GDP annual totals, registered deaths and many international comparisons, unlike the April to March financial year.
• Tax year
  The UK personal tax year runs from 6 April to 5 April the following year. It differs from the government's financial year, which runs from 1 April.
• Academic year
  The year used in education statistics: usually September to August for schools and August to July for universities.
• ITL regions (International Territorial Levels)
  The UK's official system of statistical regions, which replaced the EU's NUTS system. ITL1 is the nine English regions plus Scotland, Wales and Northern Ireland.
• Lower layer super output area (LSOA)
  A small statistical area in England and Wales, typically home to 1,000 to 3,000 people, used to publish local data such as deprivation and census results.

Parliament and elections

How laws are made, how MPs vote and how elections are won: the parliamentary and electoral terms behind claims about votes, majorities and party funding.

• First past the post
  The voting system used for UK general elections: each constituency elects one MP, and the candidate with the most votes wins, even without a majority.
• Short money
  Public funding paid to opposition parties in the House of Commons to help them carry out their parliamentary work.
• Statutory instrument
  A type of secondary legislation made by ministers using powers in an Act of Parliament, often used to set detailed rules, rates or start dates.
• Royal Assent
  The monarch's formal agreement that turns a bill passed by Parliament into an Act. Parts of the Act may still not be in force until later.
• Second reading
  The first full debate on the main principles of a bill in the House of Commons or House of Lords, usually ending in a vote if opposed.
• Working majority
  The number by which a government's MPs outnumber all other MPs who actually vote, after allowing for the Speaker, deputies and MPs who do not take their seats.
• By-election
  An election held to fill a single vacant seat between general elections, for example after an MP resigns, dies or is removed by a recall petition.
• Turnout
  The share of registered voters who voted in an election. Small differences in how it is calculated can change the figure.
• Swing
  A measure of how far support has moved between two parties since a previous election, usually the average of one party's gain and the other's loss.
• Division (vote in Parliament)
  A formal recorded vote in the House of Commons or House of Lords, in which members' names are listed by how they voted.

Crime and justice

The measures used in crime, policing, courts and prison statistics, and why recorded crime, survey estimates and outcomes can tell different stories.

• Police recorded crime
  Crimes reported to and recorded by the police, following national counting rules. It reflects reporting and recording practice as well as crime itself.
• Crime Survey for England and Wales (CSEW)
  A large household survey asking adults about crimes they experienced in the last year, whether or not they reported them to the police.
• Clearance rate (crime outcomes and charge rate)
  How often recorded crimes are solved or result in a suspect being charged. In England and Wales this is published as crime outcomes, including the charge rate.
• Proven reoffending rate
  The share of offenders who commit another offence within a year that leads to a court conviction or caution. Published by the Ministry of Justice.
• Remand
  Holding a defendant in custody before trial or sentencing. People on remand are counted in the prison population even though they have not been sentenced.
• Prison operational capacity
  The maximum number of prisoners a prison or the whole estate can hold while maintaining good order, security and the proper running of the regime.
• Custodial sentence
  A sentence that sends an offender to prison or a young offender institution. Most adults serve part of the sentence in custody and the rest on licence in the community.
• Community order
  A sentence served in the community, with one or more requirements such as unpaid work, a curfew or treatment, instead of prison.

Housing, energy and the environment

Housing tenures, homelessness duties, house building measures, fuel poverty and the emissions accounting behind net zero.

• Affordable housing
  In English planning policy, a defined set of tenures for people whose needs are not met by the market, including social rent, affordable rent and some low-cost home ownership.
• Social rent
  Rented homes owned by councils or housing associations, with rents set using a government formula and usually well below market rents.
• Affordable rent
  A type of social housing in England where rent can be set at up to 80% of the local market rent, including service charges.
• Temporary accommodation
  Housing that councils provide to homeless households while they wait for a settled home, such as hostels, bed and breakfasts or leased flats.
• Main housing duty
  The legal duty on an English council to secure accommodation for a homeless household that is eligible, in priority need and not intentionally homeless.
• Net additional dwellings
  The annual increase in England's housing stock: new builds plus conversions and changes of use, minus demolitions.
• Housing starts and completions
  Quarterly counts of new homes begun and finished, based mainly on building control inspections. Faster than the annual net supply figure but less complete.
• Net zero
  The UK's legal target for 2050: greenhouse gas emissions reduced so far that any remaining emissions are balanced by removals from the atmosphere.
• Carbon budget
  A legal cap on the total greenhouse gases the UK can emit over a five-year period, set under the Climate Change Act on the advice of the Climate Change Committee.
• Territorial and consumption emissions
  Territorial emissions count greenhouse gases produced within the UK. Consumption emissions count those caused by what UK residents buy, wherever in the world they are produced.
• Carbon dioxide equivalent (CO2e)
  A common unit that converts different greenhouse gases into the amount of carbon dioxide that would cause the same warming.
• Low Income Low Energy Efficiency (LILEE)
  The official measure of fuel poverty in England: a household with an energy efficiency rating of band D or below and income below the poverty line after housing and energy costs.

Schools and education

School performance measures, key stages, absence, special educational needs and disadvantage: the terms used in education statistics for England.

• Attainment 8
  A measure of GCSE-level results in England, adding up a pupil's points across eight qualifications, with English and maths counted double.
• Progress 8
  A value-added measure for secondary schools in England, comparing pupils' GCSE-level results with those of pupils nationally who had similar results at age 11.
• Key stages
  The stages into which compulsory schooling in England is divided, from key stage 1 (ages 5 to 7) to key stage 4 (ages 14 to 16).
• Education, health and care plan (EHCP)
  A legal document in England setting out the support a child or young person up to age 25 with special educational needs must receive.
• Persistent absence
  Pupils in England who miss 10% or more of the school sessions they could attend. Missing 50% or more is called severe absence.
• Disadvantage gap
  The difference in attainment between disadvantaged pupils and other pupils. In England it is published as the disadvantage gap index.
• Pupil premium
  Extra funding for state schools in England for each disadvantaged pupil, such as those eligible for free school meals in the past six years or who are looked after.
• English Baccalaureate (EBacc)
  A school performance measure in England showing how many pupils take GCSEs in English, maths, sciences, a language and history or geography.