As a consequence of the 2011 referendum, where New Zealand voted to retain MMP, the electoral commission had a responsibility to review MMP and to recommend to Parliament any ways in which it thought, after public consultation, how the system of MMP might be improved. Our findings are contained in our commission report on the review of the MMP voting system, which was tabled in the New Zealand Parliament in October 2012. We've provided a copy to the committee, so it should be available to you. We discuss the question of overhang seats on page 20 of that report.
On July 26th, 2016. See this statement in context.