A study says the adoption of the MMP voting system has meant more women are becoming MPs.
Lobby group Campaign for MMP has studied electoral patterns since the last first-past-the-post election in 1993.
There will be a referendum on the electoral system next year, and one of the researchers, academic Ana Gilling, says to drop MMP would be a step backwards for women.
She said in 1993, women made up about 21% of MPs. That rose to 29% in the first MMP election.
The researchers says a number of recent women-friendly pieces of legislation, such as paid parental leave, are attributable to MMP coalition governments.
