The Mainichi answers some common questions readers may have about electoral reform, which has been facing a backlash from political parties that could lose seats.

Question: How big is the disparity in the value of one vote in a House of Representatives election?

Answer: In the lower house election in 2009, the number of eligible voters in the Chiba No. 4 constituency was 2.3 times that of the Kochi No. 3 constituency. According to the basic resident register, the voter population gap in the two electoral zones widened to 2.48 times as of the end of March this year.

Q: How much disparity would become a problem?

A: In the past, when the multiple-seat constituency system was being adopted, the Supreme Court ruled a disparity of at least three times unconstitutional. When the current single-seat constituency system was introduced in 1994, the Act for Establishment of the Council on the House of Representatives Electoral District provided that in principle the disparity in the value of one vote should be no more than twice. If there is a large gap in the value of one vote, that would run counter to the Constitution's guarantee of equality under the law. Such disparities can be detected through the results of the national census and other surveys, based on which efforts to rectify the disparities are to be made.

Q: Efforts to correct such disparities have faced difficulties in the past, too, haven't they?

A: The lower house has revised the law to rectify the disparities in the vote value five times since the end of World War II. Lawmakers who faced a loss of their electoral bases due to the rezoning of constituencies opposed such moves, but the Diet managed to pass the revisions by a majority vote of the ruling bloc and part of the opposition parties. The court decisions have been taken seriously.

Q: So, we've been witnessing an unusual development now?

A: The Supreme Court has heretofore ruled the disparities in the vote value unconstitutional four times. In just one of these cases, a lower house election was called without rectifying the disparities. Then Prime Minister Yasuhiro Nakasone dissolved the lower house only three weeks after the top court ruled the disparities in the vote value unconstitutional in November 1983. It was around the same time the Tokyo District Court found former Prime Minister Kakuei Tanaka guilty for taking bribes over the purchase of Lockheed passenger aircraft. Later, measures to correct the disparities were taken before the next lower house election in 1986, and the Supreme Court did not call the case into question.

Q: They may well face trouble if they were to drastically change the electoral system and reduce the number of Diet seats like this time, mayn't they?

A: A drastic reform requires time, and the reduction of proportional representation seats faces opposition from small- and medium-sized parties that are certain to lose seats. When the system combining single-seat constituencies and proportional representation blocks was introduced in 1994, the ruling coalition comprising small- and medium-sized parties initiated the reforms, so things went exceptionally smoothly. In 2000, when the proportional representation seats were reduced by 20, the then opposition Democratic Party of Japan fought for a reduction of 50. The Japanese Communist Party and other small- and medium-sized parties were absent from the plenary session to protest the reduction itself, and the revision was rammed through by a majority vote of the then ruling coalition of Liberal Democratic Party, Liberal Party and Komeito.

Q: How about the situation overseas?

A: In Italy and New Zealand, national referendums were held prior to electoral reforms in 1993. In Britain, the model for Japan's single-seat constituency system, a national referendum held in 2011 voted down a review of the current election system. It seems many countries seek public approval before drastically changing the system. (Answers by Takenori Noguchi, Tokyo Political News Department)