SUPREME COURT/VOTING: “In October, when the Supreme Court heard arguments in a case that could reshape American politics, Chief Justice John G. Roberts Jr. registered an objection. There was math in the case, he said, and it was complicated… The statistics in the recent gerrymandering cases were more complicated, but not by much. Just as comparing registration rates between black and white voters yielded a ‘racial gap,’ comparing the voting power of Republican and Democratic voters yields what the challengers in the Wisconsin case called an ‘efficiency gap.’
The efficiency gap is a measure of the consequences of the two basic ways of injecting partisan politics into drawing legislative maps: packing and cracking.
Packing a lot of Democrats into a single district, for instance, wastes every Democratic vote beyond the bare majority needed to elect a Democratic candidate. Cracking Democratic voters across districts in which Republicans have small majorities wastes all of the Democratic votes when the Republican candidate wins.
The difference between the two parties’ wasted votes, divided by the total number of votes cast, yields an efficiency gap.
At the argument of the Wisconsin case in October, Chief Justice Roberts mocked the efficiency gap, referring to it by its initials, and suggested that it was fiendishly complicated.”
-Adam Liptak, “A Case for Math, Not ‘Gobbledygook,’ in Judging Partisan Voting Maps,” The New York Times online, Jan. 15, 2018