Heard the one about the state agency that mislaid 100,000 people? Unfortunately it's no joke. Yesterday's preliminary census results, which show that the CSO underestimated the population of Ireland by 100,000 people, raise serious questions about the operation of the organisation, with the blunder likely to result in the under-provision of many social services including health and education.
Most countries, including the United States and Britain, only count their populations once every 10 years. Ireland is relatively unusual in doing so twice a decade, with the last census having been held in 2006. Since then the CSO has published annual population estimates, with the most recent one, which was published last September, putting the population at 4.47 million people in April 2010.
So imagine our surprise when the preliminary census results were published yesterday. These show that the population was actually 4.58 million in April 2011. In other words, there were 100,000 more people in the country than the CSO had estimated. That's the equivalent of more than one in 50 of the entire population.
If Ireland only held a census once every 10 years such a miscalculation might be just about forgivable. But the notion that 100,000 people, the equivalent of the entire population of Co Kilkenny, could go "missing" in the space of just five years is hard to fathom.
Put it another way. The population of Ireland increased by 342,000 between the 2006 census and 2011 census as against the increase of approximately 240,000 which the CSO had been estimating, which means that the actual population increase was more than 40pc greater than the CSO's guesstimates.
And this is more than just an obscure academic point of interest solely to statisticians. Far from it. Knowing how many people there are and where they live is critical to providing schools, hospitals, roads, housing, water, sewage, gas, electricity and a raft of other vital services. Get it wrong, as the CSO has, and tens of thousands of people will be condemned to sub-standard services and over-crowded facilities.
So how did the CSO manage to get its population estimates so very wrong? With the number of deaths and births being readily available it is clear that the population under-estimate was due to the CSO's failure to gauge the level of emigration and immigration correctly. What seems to have happened is that far more people than expected came to this country in the early part of the 2006-11 period and that fewer people than expected left in the latter part of that period.
While the CSO would no doubt argue in its defence that trying to accurately estimate such population flows is exceptionally difficult, the fact remains that all of us will end up paying for its failure to get it right. The CSO must move quickly to determine what went wrong and ensure it isn't announcing another population blunder when the results of the 2016 census are published.