Question to the Cabinet Office:

To ask Her Majesty's Government what assessment they have made of the accuracy of the Office for National Statistics’ population growth forecasts when used in planning for future house building needs in green belt areas of England; and whether algorithms are used in the construction of the forecasts.

The information requested falls under the remit of the UK Statistics Authority. I have, therefore, asked the Authority to respond.

Professor Sir Ian Diamond | National Statistician

The Rt. Hon, the Lord Patten of Barnes

House of Lords

London

SW1A 0PW

20 May 2021

Dear Lord Patten,

As National Statistician and Chief Executive of the UK Statistics Authority, I am responding to your Parliamentary Question asking what assessment has been made of the accuracy of the Office for National Statistics population growth forecasts when used in planning for future house building needs in green belt areas of England; and whether algorithms are used in the construction of the forecasts (HL79).

The Office for National Statistics (ONS) publishes population estimates and the methods used are set out in the Mid-year Population Estimates Quality and Methodology Information paper.[1] Similar quality and methodology information papers are published for national population projections[2], subnational population projections[3] and household projections[4]. Each round of our mid-year population estimates and population projections is fully quality assured and where appropriate (such as for subnational outputs) includes reviewing differences between local authorities and small geographies.

The ONS’ projections are not forecasts but are based on the continuation of recent trends and do not take into account social or economic factors that could affect the population in the future. As such, they do not try to predict any potential demographic consequences of future political or economic changes.

Individual local authorities have responsibility for planning future housing needs through their own local plans. The Ministry for Housing, Communities and Local Government (MHCLG) are responsible for setting out guidance and policy on the use of ONS statistics for the purposes of planning.

You may be aware of the recent Office for Statistics Regulation report[5] about the ONS’ population projections and estimates, which found that at the national level, the ONS’ approach to projections and estimates was fit for purpose. The ONS has published a National Statistical blog explaining how the Centre for Ageing and Demography (responsible for population estimates and projections) at the ONS will meet the challenges raised by the report[6].

Yours sincerely,

Professor Sir Ian Diamond

[1]https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationestimates/methodologies/midyearpopulationestimatesqmi

[2]https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationprojections/methodologies/nationalpopulationprojectionsqmi

^[3]https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationprojections/methodologies/subnationalpopulationprojectionsqmi

[4]https://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/populationprojections/methodologies/householdprojectionsinenglandqmi

^[5]https://osr.statisticsauthority.gov.uk/news/osr-publishes-its-review-of-population-estimates-and-projections-produced-by-the-office-for-national-statistics/

^[6] https://blog.ons.gov.uk/2021/05/17/meeting-the-challenges-in-population-estimation/