The urban borough elections result for first preference votes were:
Sinn Féin 27%
Labour Party 18%
Other nationalists 15%
Proportional Representation (PR) is used in Ireland for the first time in the local elections of 1920. PR differs from the widely used first past the post voting system in that the seats won tend to be representative of total votes cast thus encouraging participation even from minority communities. In the 1921 Northern Ireland general elections, when PR was used, every seat was contested. However, after Northern Ireland reverted to first past the post system, numerous seats went uncontested by nationalists who knew they had no chance of winning seats. In the 1933 general election, fought under the British first past the post system, only 19 of 52 seats were contested. Gerrymandered voting districts plus first past the post saw Unionists gain 36 of 52 seats in the election. this can be contrasted with the 1920 local elections when Sinn Fein won control of 10 of 12 urban councils.
Read PR in Ireland: http://proinsias.net/publications/pr_in_ireland/2006/08/why-ireland-chose-pr.html