Realising the historical value of the Irish Censuses of Population

Since 1841 the periodic Census of Population has been the cornerstone of official statistics in Ireland, particularly in the context of providing comprehensive information on demographic and social conditions. While some efforts were made to undertake censuses prior to 1841 they are generally considered to have been of poor quality for various reasons.

From 1841 to 1911 inclusive, censuses were conducted every decade, in years ending in a ‘1’. Similar censuses were conducted in the other countries of the then United Kingdom of Great Britain and Ireland. No census was undertaken in 1921 due to the unstable security situation surrounding the Irish War of Independence. Following the establishment of the new independent Irish State in 1922, periodic censuses were re-introduced in 1926 and repeated in 1936 and 1946. In 1951 the frequency of census taking was increased to once every five years, in years ending in a ‘1’ and ‘6’. This frequency has been maintained up to the current time with a small number of exceptions including the postponement of the 2021 census to 2022 because of the Covid-19 pandemic.

The detailed reports published for each census provide a rich source for tracking the evolution of the Irish population over the past 180 years at national, regional and local levels. Up to the recent censuses the sole, or predominant, mode of dissemination was the publication of hardcopy paper reports. Luckily, all these reports have been preserved and can now be readily accessed online. In more recent years, the focus has shifted towards more flexible electronic dissemination, including electronic databases, interactive maps and samples of anonymised records.

Emigration and immigration

Demographers and historians, amongst others, have therefore had a rich source for tracking the development of the Irish population, which has many striking and almost unique features. In particular, the impact of external migration on the population has been very notable over the entire period. Between 1841 and 1961 the population of the Republic of Ireland declined from 6.5 million to just 2.8 million due to substantial and persistent emigration.

The population has since recovered to stand at close to 5 million at present. Inward migration over the past 25 years has contributed significantly to the recovery. As a consequence of the latter, the percentage of non-Irish born recorded in the Census has increased from around 2 per cent in 1991 (mainly the children of returning Irish emigrants) to over 17 per cent in 2016 with a worldwide spread of nationalities.

Increasing scope but limited resources

While the basic objective of the census, namely the complete enumeration of the population, has remained the same over time, there have been significant changes in both the scope of the information collected and in the range of analyses produced. In general, the scope of census has increased over time and this was documented for the censuses undertaken between 1841 and 1991 inclusive by Linehan in a paper to the Statistical and Social Inquiry Society of Ireland in 1991.

This, of course, impacted in turn on the range of statistical results that could potentially be produced for each census. However, there was an additional factor that constrained the statistical outputs produced for the earlier censuses: the need to manually produce the analyses. Not only was this labour and time intensive, but it was also necessary to define in advance all the tables to be produced and to then put in place appropriate manual extraction, summarisation and aggregation procedures to obtain the desired statistical results.

This of course ruled out the production of additional or ad-hoc tables, which are common features of modern censuses, as it would have been necessary in most cases to start from scratch to produce them!

New insights with modern methods

The latter factor, mentioned above, raises the interesting question as to what additional analyses and insights might be derived if the basic returns from the earlier censuses could be processed using modern information technology.

Recent work undertaken by The Sensible Code Company in respect of the 1901 and 1911 censuses may provide an answer to this question. Under the Irish Statistical Law 1993 the individual statistical census returns cease to be subject to statistical confidentiality after 100 years and can be accessed without restriction via the National Archives for genealogical and other research. The 1901 and 1911 census forms are publicly available online.

In order to obtain a dataset to demonstrate its Statistical Disclosure Control software, Cantabular, the Company scraped the National Archives website and successfully downloaded the individual returns from the two censuses. The Company is now working with the Irish Central Statistics Office to see whether the resultant database, following some additional coding and assessment, can be used to generate new good quality analyses from the two censuses.

Should a successful outcome be obtained, and the initial indications are promising, then an efficient procedure for generating additional statistical and historical value added from the early censuses will have been demonstrated.

Clearly, the current project has been facilitated by the lifting of the statistical confidentiality constraint after 100 years in Ireland and the availability of the original census returns in electronic form on the National Archives website.

However, many National Statistical Institutes may still have access to original census returns, either in paper or electronic formats, and thus the possibility to replicate the essence of the The Sensible Code Company project and make earlier censuses amenable to modern processing possibilities.