of the Supreme Court ruled that the maximum discrepancy of 2.30 in voting weight between the Kōchi 3 and Chiba 4 constituencies in the 2009 election was in violation of the constitutionally guaranteed equality of all voters. As in previous such rulings on unconstitutional elections (1972, 1980, 1983 and 1990 Representatives elections, 1992 Councillors election), the election is not invalidated, but the imbalance has to be corrected by the Diet through redistricting and/or reapportionment of seats between prefectures. In 2016, a panel of experts proposed to introduce the [John Quincy] Adams apportionment method (method of smallest divisors) for apportioning House of Representatives seats to prefectures. The reform is planned to be implemented after the 2020 census figures are available and not expected to take effect before 2022. In the meantime, another redistricting and apportionment passed in 2017 is designed to keep the maximum malapportionment ratio in the House of Representatives below 2. In the FPTP tier, it changes 97 districts and cuts six without adding any; in the proportional tier, four "blocks" lose a seat each; the total number of seats in the lower house is cut to 465, 289 majoritarian seats and 176 proportional seats. The malapportionment in the 2010 and 2013 regular House of Councillors elections was ruled unconstitutional (or "in an unconstitutional state") by the Supreme Court, and has been reduced by a 2015 reapportionment below 3 (at least in government statistics from census data which is regular and standardized but lags behind resident registration statistics and the actual number of eligible voters; using the latter, the maximum malapportionment in the 2016 election remained slightly above 3). The following table lists the 10 electoral districts with the highest and lowest number of registered voters per member elected for each chamber of the National Diet according to the voter statistics as of September 2016 released by the Ministry of Internal Affairs and Communications – it takes into account the lowering of the voting age and the district reforms to both houses of the Diet in effect since the 2014 and 2016 elections, but not the 2017 redistricting/reapportionment effective from the next House of Representatives election. Prefectural and local elections Unified local elections (統一地方選挙 tōitsu chihō senkyo) are held once every four years. Prefectural assemblies and governors, as well as mayors and assemblies in municipalities, are elected for four-year terms. In April 1947, all local elections in the 46