2021 Census provides an accurate picture of our population

/ Author: Gerben Stolk
© Hollandse Hoogte / Co de Kruijf
Once every ten years, there is a special day within CBS: the day when, after a long and concerted effort, the most recent census is finalised. Thursday 28 March 2023 was another such a day. This time, the census in question was the 2021 Census, which provides an extremely accurate picture of the population of the Netherlands. As project leader Eric Schulte Nordholt puts it: ‘It’s a huge achievement for a relatively small team like ours, which has once again been able to deliver so much high-quality data to the European statistics office Eurostat and on time.’


How many people live in the Netherlands? What is the gender, age and marital status of each of those individuals? Two examples of the type of information that any census needs to provide. In our country, censuses are carried out by CBS. Indeed, the census is one of CBS’s fundamental responsibilities, says Schulte Nordholt, project leader and international coordinator of the Main Directorate for Socio-economic and Spatial Statistics (SER). ‘CBS was established in order to make the 1899 Census possible. Since then, it has become a CBS tradition, every ten years.’

Support from government

‘The purpose of a census is to provide accurate data for all levels of government,’ Schulte Nordholt continues. ‘How many schools, hospitals and nursing homes are required? When decisions of this kind are made, it is important that they are based on accurate information. Following World War II, the need for information at the European level also developed. For this reason, the 27 member states of the European Union (EU) send their census statistics to Eurostat every 10 years. This enables them to see how they compare in certain areas. What are we doing well and where are improvements possible? This kind of data is also very valuable for EU policy.’

Population register

Every country provides data on the same subjects and according to the same principles. However, the data collection methods can vary, Schulte Nordholt explains. ‘In the Netherlands, we have good infrastructure with registers available at CBS that can be linked together – the System of Social Statistical Datasets. The backbone is the Personal Records Database (BRP), which is essentially a population register. This includes every person’s date of birth and marital status, for example. Digital data are also available on housing in the Netherlands, which are used in the 2021 Census. Partly as a result of this, we can get the job done with a smaller team than other countries. There, statistical staff visit people in their homes to complete questionnaires, or lists are sent out by mail and the completed copies are then scanned.’

Information on occupations and education

The 2021 Census also includes information on occupation and education. Sources other than the Personal Records Database were tapped for that purpose, explains statistical researcher Irene Kuin. ‘CBS conducts its Labour Force Survey (EBB) on an ongoing basis. Around one percent of workers provide information about their occupation and education in that way. And when it comes to education, we supplement that with data from the registers of the Employee Insurance Agency (UWV) and Education Implementation Service (DUO), among others. As far as occupations are concerned, however, we had no additional data available – only the EBB. For this reason, we weighted the limited data that were available on occupations, which enabled us to convert it into a representative picture of the entire population.’

New legislation

The process of delivering a census consists of two broad phases: preparation and execution. Regarding the first phase, Schulte Nordholt says: ‘Every census is rooted in European legislation. In the years leading up to the actual collection of data, a minimum set of requirements that countries need to meet for the next census is determined at the European level. For example, which variables, tables and categories should be included? What standard of quality does the data need to meet? For the last few censuses, I was involved in determining the new legislation on behalf of CBS.

Census Day

In 2021, the legislation applicable for the census was known for that year. The official date for the census was 1 January, also known as ‘Census Day’. After the new legislation had been enacted, a team was established within CBS to carry out the census. From that date on, five staff members met every week to coordinate progress, while around 25 colleagues began implementing subprojects. Eric Schulte Nordholt and Martine de Mooij were the project leaders.

The CBS team that worked on the results of the 2021 Census
© Sjoerd van der Hucht

New features

The 2021 Census has a number of new features. This includes looking at the population in squares measuring one kilometre by one kilometre. Schulte Nordholt: ‘Generally the population is measured within a given municipality, region or province. But boundaries can change. Municipalities can merge, for example, giving them a larger population. If this happens between two censuses, the data can no longer be compared. Squares measuring one kilometre by one kilometre are not subject to boundary changes, which is why the census is now also carried out on this scale.

Better comparisons

Schulte Nordholt explains: ‘A grid of squares measuring one kilometre by one kilometre was laid across Europe. In the Netherlands, there are 39 829 of those squares. This enables better comparisons to be made within Europe. For example, France has nearly 35 000 municipalities while the Netherlands less than 350; in the Netherlands, the average municipality has many more inhabitants. Sometimes, then, it makes more sense to compare squares of equal area than municipalities.’

X-Y coordinates for dwellings

CBS used the X-Y coordinates of each person’s home based on using address data. These were incorporated into the squares. Kuin: ‘One square kilometre is a small area and sometimes not many people may live there. That meant that we had to make absolutely sure that no information relating to specific individuals was disclosed. We had to exclude the possibility that, for example, a country of birth in a given square could be traced back to a specific individual.

Combining dimensions

Another exciting new feature of the 2021 Census is that there are 41 tables combining various ‘dimensions’. Each table has a different combination of dimensions. Kuin: ‘For instance, there is a table where you can see how many men work in a given occupation within a certain region and their ages. 32 of the tables are about people, and the other tables are about households or dwellings. The tables have slightly fewer dimensions than the tables from the previous census, but the main innovation concerns how they were created.’

An accurate picture

‘The more detailed the tables, the higher the risk that data could be traced back to residents,’ explains Kuin. ‘That is something that we have to prevent. In the previous census, therefore, some data were omitted, which was a great shame for users. This time, we were able to publish more detailed data in the tables. To do this, we moved some data up or down slightly. In addition, some individuals with certain characteristics were switched between geographic areas. To use technical jargon, we added some noise in order to avoid disclosure. The tables do not reveal anybody’s individual data, but they do provide a reliable picture of individuals, households and dwellings in the Netherlands.