There has been a call for all councils to adopt STV voting as a way to avoid voters' confusion when confronted with ballot papers.
Just seven of 78 councils and all 20 district health boards use Single Transferable Voting, in which voters number candidates in order of preference.
The majority of voters are faced with ballot papers containing both voting systems.
There is evidence that voting forms showing a First-Past-the-Post (FPP) option for mayor or council, but STV for the DHB attract a higher number of invalid votes.
Electoral Officer Warwick Lampp says an average of 8% of DHB ballot papers are invalid, compared with 1% for FPP.
However, where all voting is STV, the disallowed votes are on a par with FPP.
Janine Hayward, an associate professor of politics at the University of Otago, says using STV for all councils would improve voter turnout.
Local Government New Zealand says it has no view on STV, although it would be simpler if there was only one voting system.
Voting for Palmerston North City Council was by STV this year for the first time, and re-elected mayor Jono Naylor says feedback is that some of the public struggled to understand it.
Mr Naylor said the council thought it was a fairer system but there will need to be some analysis. He says the next step is to analyse how many people got the voting system wrong and whether or not votes were missed because of it.