The differing age profiles of Northern Ireland’s Protestant and Catholic communities are key to understanding the region’s shifting demography, the head of the census has said.

Dr David Marshall, director of census and population statistics at the Northern Ireland Statistics and Research Agency (Nisra), said the Catholic community was on average younger than the Protestant one.

“The religious demography of Northern Ireland in part is driven by age structures,” he said.

“What we found in the 2011 census was that the Catholic population was on average younger, so there was essentially a higher number of births in the Catholic population than deaths.

“That acted to increase the size of the Catholic population from 2011 to 2021.

“The converse is true for the Protestant population. On average, it was older 10 years ago and what we’ve found is that there’s more deaths than births in the Protestant population, and that acts to bring the Protestant population down in number.

“There are other factors as well but those are the two key things.”

Dr Marshall said research following the 2011 census also found evidence of an increasing number of people who would have previously described themselves as Protestant choosing to identify as having no religion.

He said there was a “fair chance” that trend had continued and was also a contributory factor to the falling Protestant population recorded in the latest census.

Dr Marshall said a surge in the number of people holding Irish passports in Northern Ireland was influenced by Brexit.

“Clearly, in part that’s driven by the impact of the United Kingdom leaving the European Union in 2016,” he said.

“Indeed, the Department of Foreign Affairs in Dublin has indicated additional demand for passports from people living here in Northern Ireland.”

Dr Marshall said the key message from Census 2021 was the increasing diversity it showed across Northern Ireland.

“We published today detailed information on country of birth, ethnicity, languages, nationality – all of those statistics point to a more diverse Northern Ireland than ever before,” he said.

“One point of interest would be the population of Belfast has increased from the 2001 census to the 2021 census – all of that increase over 20 years is down to people who are in the ethnic minority group.

“The white population of Belfast hasn’t changed dramatically over the last 20 years. It’s the ethnic minority groups.”