Interreligious unions are increasing in Canada but the great majority of marriages or common-law relationships still consist of partners from the same religious affiliation, Statistics Canada says.

A new study released Tuesday based on census data showed of the 14.1 million Canadians who were couples in 2001, 19 per cent or nearly 2.7 million had a partner from a different religious group.

That's upfrom 15 per cent in the 1981 census.

More than half of these unions were between Catholics and Protestants, the two largest religious groups in the country.

The study found the likelihood of an interreligious union depended upon where you lived, how homogeneous the religious mix of your community was, how religious you were, how traditional the doctrine of your religion was and how long you had been in Canada.

About 13 per cent of people affiliated with conservative Protestant religious groups reported being in an interreligious union, compared with 23 per cent of "mainline" Protestants and 27 per cent of Catholics outside Quebec.

The number of such unions between people citing Islam, Sikhism and Hinduism as their religion declined between 1981 and 2001.

The study attributed the drop to increased immigration by these groups between 1991 and 2001, making it more likely for them to have a strong cultural association with the marital traditions of their country of origin.

The percentage of the population reporting no religious affiliation more than doubled from seven per cent in 1981 to 17 per cent in 2001.