However, the Electoral Reform Society, which commissioned the study, said what voters do with their later preferences is "more diverse and interesting".
This survey was carried out in the months following last May's assembly election.
More than 4,000 people were interviewed for the survey.
About 2,000 of the interviewees filled out mock ballot papers.
Not surprisingly, the survey found that the vast majority of voters backed parties traditionally associated with their own community.
Only 4% of Catholics gave a unionist a first preference vote, while only 2% of Protestants picked a nationalist.
About a fifth of both Protestants and Catholics gave their first preferences to a cross community or centrist party, the survey indicated.
When later preferences were included the figures rose, but only slightly, with an estimated 8% of Catholics prepared to give a unionist a vote and 6% of Protestants putting a number against a nationalist box.
In the forthcoming assembly election, depending on where you live, you have a choice of between nine and 15 candidates - but according to this survey the average voter only backs three or four politicians on their ballot paper.
Some 80% of voters in Northern Ireland give their first preference votes to parties associated with their own community, according to a new survey.