The Catholic population of Northern Ireland could possibly exceed that of the Protestants by 2021, a leading researcher has claimed.

Northern Ireland has traditionally been a Protestant majority country, but Dr. Paul Nolan, who focuses on social trends in the region, believes that it could change in just three years.

"Three years from now we will end up, I think, in the ironic situation on the centenary of the state where we actually have a state that has a Catholic majority," he told the BBC.

A census conducted in 2011 indicated that Protestants only outnumber Catholics by three percentage points at 48-45 percent.

A recent figure has reportedly shown that 44 percent of people who are of working age are now Catholics, compared to 40 percent who are Protestants. Among school children, 51 percent identify as Catholics, while 37 percent are Protestants. Protestants only outnumber Catholics among people over the age of 60 at 57-35 percent.

Nolan said, however, that the decline of Protestants did not necessarily correlate with an increase in support for a united Ireland.

He said that among those who identify as Catholics in the 2011 census, only 25 percent affirmed their exclusively Irish identity.

When asked about polls showing support for a united Ireland, Nolan said that the surveys are asking the wrong question.

"If we got to the situation where people go into a polling booth and have to put the mark against a united Ireland, it's very hard for anyone to predict it. Just ask Hillary Clinton, ask David Cameron, ask Theresa May: were they right to put their faith in the opinion polls? I don't think so," he told the BBC.

Disputes between Protestants and Catholics have been a part of Northern Ireland's history since it separated into two nations in 1921.

The religious conflict turned violent in the 1960s and lasted through 1998, a period which came to be known as "The Troubles." At least 3,500 people have been killed and 50,000 people injured in the conflict, according to CNS News.

A peace deal, known as the "Good Friday Agreement," was struck in 1998, but tensions have occasionally flared between the two sides since that time.