The plaintiffs’ argument in the state lawsuit over Pennsylvania’s congressional district map hinges on whether they can prove the state legislature designed a map meant to dilute Democratic votes. Much of the trial’s third day was spent by plaintiffs trying to quantify the map’s alleged partisan advantages by looking at decades of data, spurring a debate about how many votes are “wasted” because of the way congressional boundary lines were drawn. Say you have five congressional districts each with 100 voters. Democrats win two by wide margins, and Republicans win three in tight races. That’s what redistricting experts would call a map with an “efficiency gap” designed to advantage Republicans by wasting votes for Democrats.
Political scientist Christopher Warshaw testified for the plaintiffs Wednesday that Pennsylvania’s efficiency gap, favoring Republicans, is the currently the widest in the nation.
“The efficiency gap is really capturing the heart of gerrymandering: translating votes into seats with as few votes as possible,” Warshaw said.