Explaining the efficiency gap

Projected Republican

seat share

Actual seat share

Efficiency gap

In Wisconsin, Republicans gained a much greater share each election than the district-by-district vote suggests....

Wisconsin statehouse elections

45.1%

60.6

2012

58.0

63.6

2014

55.4

64.6

2016

...while in Illinois, the actual seat shares aligned closely with the projections.

Illinois statehouse elections

2012

39.8%

42.1

2014

39.8

42.8

2016

41.5

43.2

Notes: Projected seat shares were calculated using the formula by Stephanopoulos and McGhee. Uncontested races were adjusted to a 75%-25% split to more accurately estimate the projected share, as suggested by Stephanopoulos and McGhee.
Data: Illinois Board of Elections, openelections.net
Credit: Better Government Association