The census on Sunday week will be the 27th in a regular series that began almost 200 years ago in 1821. Throughout the 19th century a census was undertaken every 10 years. Because of the War of Independence in 1921, that census was postponed to 1926. Since 1946, because of its value for planning for our economic and social needs, we have held a census nearly every five years.

The census was the first and only comprehensive set of statistical data for Ireland in the first half of the 19th century. In the early censuses, there was a focus on collecting data on births and deaths, as well as the collection of information on the religion of the population and the condition of the housing stock.

From the early censuses, data was collected on the educational attainment of the population. However, while in the 19th century the focus was on literacy, today considerable detail is collected on the level and nature of individuals’ qualifications.

The census is an expensive undertaking because it covers the whole population. However, for a range of purposes, the data it collects is invaluable. No other survey could hope to capture the level of detail necessary for certain important policy purposes, especially where regional or minority groups are involved.

Since its inception, the census has provided the basis for understanding how the population is growing, where people are living and the movement of the population in the country and outside it. Without the census, it would be very difficult to plan for the number and size of schools needed, the number of homes that the population will require, and the location and nature of the services needed for an ageing population.

Over the last decade, census data has been used for a range of new important tasks that help us understand some of the policy challenges that Ireland faces.

The CSO linked the 2006 census data to the data on deaths in the subsequent year, which gave us very valuable information on life expectancy for different groups of people.

It highlighted a major problem of premature deaths, especially among young males with very limited education, something that could not have been identified from other data sources.

Population patterns

The information on where everyone lives can be linked to their employer’s address to give pretty comprehensive information on commuting patterns. When linked to other data on how the structure of employment is changing, this can give valuable information on future transport needs.

A third important area where the census can provide comprehensive information is on people with disabilities. Because those affected are spread throughout the population, the use of surveys to collect data would be pretty unsatisfactory – too few people with disabilities would appear in a random sample of reasonable size.

In recent decades, a vital area of information provided by the census, which would be difficult to collect through other means, has been details on the characteristics of returning emigrants and immigrants.

In the last few years, the records of the 1911 census have been released and they have proved interesting for historical purposes.

For example, in 1911 two women in Ranelagh stated that their disability was that they were “unenfranchised”, having already declared their occupation as suffragist.

From an early stage in my career, I have had a certain fascination for the data provided by the census. On the night of the 1971 census, I was on a boat to Britain to support a UCD team at a competition in Manchester.

The boat was due to leave Dún Laoghaire at 11.15pm on its way to Heysham. I contacted the CSO census helpline and they reassured me that if the boat was in territorial waters at midnight everyone on the ship should be included in the census.

At midnight, I duly took bearings on the Pigeon House chimney and Howth. My conclusion was that we were still within territorial waters and I then asked the crew for my census form.

Needless to say this did not go down well and, in the end, the first officer was summoned to reassure me that we were safely on the high seas at midnight.

As a result, I did not appear in the 1971 census but reappeared as a returned emigrant in the 1976 census.

This time round I will happily fill out my form to record my presence.