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A referendum is being held to coincide with the general election on November 26.
The electoral commission is touring its referendum roadshow to 20 centres around the country.
University of Canterbury political scientist Dr Therese Arseneau told about 25 people at Forsyth Barr Stadium first they had to consider whether they wanted to retain MMP. If not, they had four other potential replacement voting systems from which to choose.
She said people should vote in both sections of the referendum, because their second choice could help determine an alternative electoral system for Parliament.