"The Irish News/Institute of Irish Studies/University of Liverpool poll shows a 1.6% increase for Sinn Fein from the Assembly election last May to lift its vote share to 30.6%."
Last year’s Stormont election saw Sinn Fein returned with the largest number of MLAs, becoming the first nationalist party in Northern Ireland to do so.
www.irishexaminer.com
By the same measure DUP managed 24%
"The poll suggests Jeffrey Donaldson’s party has slightly increased its share of the vote from last year by 2.6%, from 21.3% to 23.9%."
Given that currently Republicans hold 35 seats with a 39% of support, and Unionists aslo hold 35 seats with a 39% of support, but refuse to atend the Assemble, I'd say that Republicans represent well over half of the population.
As Sinn Fein are by far the largest Republican party, I think it's fair to suggest that they represent over 50% of the population.