In mixed-member proportional representation (MMP), what’s the difference between an overhang seat and a leveling seat?


The Wikipedia definitions sound identical to me; they are both ways to make a political party’s share of seats in the legislature more proportional to their share of the popular vote, by giving them additional seats, I guess. But they’re apparently different things?

In: 3

A leveling seat is one given to a party with **fewer** constituency seats than its proportional share.

An overhang seat occurs when a party wins **more** constituency seats than its proportional share.

Say the parliament is supposed to have 100 seats total. By popular vote, party A wins 25% of these seats, so they should get 25 seats. However, they were voted first in 30 constituencies.

So they will have 30 people in the parliament guaranteed despite only being entitled 25. These 5 additional seats are the overhang seats.

The other parties have a combined 75% percent of the popular vote, meaning they should get 75 out of 100 seats. Now that party A already has 30, this will leave the rest short of what they deserve.

In order to fix the proportions between the parties, the other parties get 15 additional seats, bringing the parliament up to 120 seats total. These 15 seats are the level seats.

Party A now has 30/120 seats, so they are back at their 25% share. But they still managed to get all their constituency winners into the parliament, despite originally winning less seats in the popular vote.