Census 2021: How do official population figures compare to estimates?

We now have more robust figures on the size and characteristics of Camden’s population.

A Census 2021 envelope ahead of all households being asked to complete the census ahead of Census Day on Sunday. Picture date: Saturday March 20, 2021.
A Census 2021 envelope ahead of all households being asked to complete the census ahead of Census Day on Sunday. Picture date: Saturday March 20, 2021.

We now have more robust figures on the size and characteristics of Camden’s population.

But how do they compare to estimates which are used by decision makers in central and local government to understand their communities’ needs?

Mid-year population estimates are produced annually by the Office for National Statistics and are based on the most recent census.

The ONS rolls forward information from registers for births, deaths and migration surveys to produce each year’s estimate – but it means the further away from the census, the more uncertain they are.

ONS statisticians estimated there were 279,516 people of all ages living in Camden as of mid-2020 – far above the 2021 census figure of 210,100.

With the latest census figure 24.8% below the estimate, it meant the area had the greatest disparity between their population predictions and official results.

But London Councils, the umbrella body representing all 32 boroughs and the City of London Corporation, said the capital's population is likely to have been "significantly undercounted", in part due to some people temporarily relocating themselves during the pandemic.

The census data, a snapshot of society across England and Wales on March 21 2021, suggests London’s total population was just over 200,000 (2%) lower than the previous population projection.

Data from the 2021 census tells us there were 24,800 (11.8%) over-65s living in Camden, compared to the 33,599 (12%) estimated by the ONS.

There are reportedly fewer males in Camden than estimated by the ONS – 2021 census results revealed 99,500 males (47.4%) were usual residents on census day, while the mid-2020 prediction was 142,915 (51.1%).

The latest estimates suggested there were 136,601 (48.9%) females in the area, but in March last year, 110,600 (52.6%) said Camden was their home.

The ONS says population statistics are “vital in making a range of decisions and informing public debate".

During the coronavirus pandemic, estimates have been used to measure vaccine uptake at a national and regional level, while they are also used to measure unemployment rates, forecast pensions and make decisions about local services – such as the number of school places of the provision of health services for an ageing population.

The 2020 mid-year population estimate for England and Wales as a whole stood at 59.7 million – very close to the 2021 census figure of 59.6 million.

The ONS noted that population change in certain areas "may reflect how the coronavirus pandemic affected people’s choice of usual residence on census day".

“These changes might have been temporary for some and more long-lasting for others," it added.

Georgia Gould, chair of London Councils, said: “Census 2021 took place during the extraordinary circumstances of the Covid-19 pandemic and a national lockdown, so this snapshot data must be treated with extreme caution.

"Accurate census data matters for Londoners because it helps determine government funding allocations to local authorities. Billions of pounds for frontline services are at stake."

She added that even small inaccuracies in population counts can "seriously undermine" future service provision, and cautioned that Londoners could end up losing out as a result.