For those who voted in recent council elections in New South Wales, it may come as a surprise to discover some preference votes may not have counted.
While voter's first preferences are counted in full, the state's electoral commission relies on computer software to distribute later preferences.
It is a system computing experts claim is deeply flawed.
Vanessa Teague, a Senior Lecturer at the University of Melbourne's School of Computing and Information Systems, said the NSW Electoral Commission uses an algorithm to extrapolate random samples.
"The NSW counting rules specify that when preference are being redistributed, rather than redistributing the whole of the candidates' pile, a random sample is taken," Dr Teague said.
"That can sometimes induce some random effect on the outcome, especially in the last few seats.
"There's a handful of councils, both in 2012 and 2016, where, when we run the election a million times with slightly different random samples, we get a couple of different possible answers, especially for that very last seat."
Bugs in the counting code
Dr Teague said there were also errors in the code used to count votes.
"Both in 2012 and again in 2016, we could see from the transcripts of how the election elimination and seating progressed ... that the code they used to count the votes actually had mistakes," she said.
"In 2012, that mistake did have an impact on at least one seat, in the council of Griffith.
"So, the combination of the bug and the random selections means there's a pretty good argument that at least one candidate who should have won a seat - about 90 per cent probability - didn't win a seat."
The source code for the count is not available for public scrutiny.
System a '1970s legacy'
NSW Greens MP David Shoebridge said the system is the "legacy" of an era when allocating preferences was considered too difficult.
"Now there's no difficulty at all, we have more than enough computer power to do it," Mr Shoebridge said.
"In fact, we have more than enough human resources to actually count the votes."
The NSW Parliament's Joint Standing Committee on Electoral Matters is currently looking at the system.
The Committee is taking submissions and is expected to hold a hearing next month.
Dr Teague said the use of similar systems had been scrapped for Senate elections and in some states.
"The Senate used to be counted this way and there was a bit of a controversy in the 70s, when they realised that random sampling made a difference," she said.
"In NSW, the old rules have never been changed."
