Missouri Uses Stephanopoulos's Formula in Gerrymandering Amendment

Missouri first to adopt fairness test against gerrymandering

The constitutional amendment approved by Missouri voters in November keeps those criteria. But it also requires a new nonpartisan state demographer to base state House and Senate districts on the votes cast in the previous three elections for president, governor and U.S. senator — races that are decided by voters statewide and are not affected by gerrymandering.

The districts must come as close as practical to achieving “partisan fairness” as measured by a formula called “the efficiency gap.”

That formula was created earlier this decade by Eric McGhee, a researcher at the nonpartisan Public Policy Institute of California, and University of Chicago law professor Nick Stephanopoulos. It compares the statewide share of the vote a party receives with the statewide percentage of seats it wins, taking into account a common political expectation: For each 1 percentage point gain in its statewide vote share, a party normally increases its seat share by 2 percentage points.

Read more at Associated Press