On December 14 2014, Japanese voters — well, about half of those eligible to vote — headed out to the polls to choose a new House of Representatives. The incumbent Liberal Democratic Party (LDP) - Komeito alliance emerged victorious, picking up an additional 20 seats to take their total to 326 seats in the 475 member House.
There are three main narratives of this election. One is of an unnecessary and uninteresting "snap" election that merely maintained the status quo. Prime Minister Shinzo Abe and his coalition were returned to power with another parliamentary supermajority, which means Abe can continue with his program of "Abenomics". A second narrative is that of historically low turnout. Turnout fell 6 percentage points from 2012, to 53% of the voting age population. (In Japan, voter registration is automatic and administered by local authorities, who add people to the register using the Juki Net register of Japanese residents.)
The third narrative is of the disproportionality between votes cast for the LDP and the constituency seats won by them. Japan uses a parallel voting system, in which every voter gets two votes: one candidate vote for a single member in their local constituency; and a second vote for regional seats, elected using party-list proportional representation in multi-member districts.
In the 180 seats elected by proportional representation, seats were -- predictably -- allocated reasonably proportionally. The LDP won 33.1% of the party list vote across Japan and received 37.8% of the seats.
However, in the 295 constituency seats, LDP candidates received 48.1% of the vote across Japan... but won 223 of the seats. That's 76% of the seats from less than half of the vote.
And so, overall, the LDP ended up with 291 (61.3%) of the 475 seats in the House of Representatives from 41% of the votes cast.
The disproportionality is due in part to malapportionment: The 295 constituencies range in size from just over 200,000 registered voters to almost 500,000. The smaller constituencies tend to be rural, where support for the LDP is strongest - and so the LDP can win more seats from fewer votes.
More importantly, the disproportionality is a consequence of the use of single-member districts with winner-take-all in the constituency seats. Single-member districts with winner-take-all are inherently susceptible to disproportionality, especially in heterogeneous populations spread out unevenly (as in Canada) or in multi-party systems (as in Japan).
Unlike in Germany and New Zealand (which use a system similar, but superior, to parallel voting called "mixed member proportional"), the Japanese system makes no attempt to achieve proportionality in the legislative chamber overall. Thus, the unfortunate effects of winner-take-all dominate Japanese election outcomes.