Document ID: ./input/supremecourt_opinions/opinions/17pdf/16-1161_dc8f.pdf
Page Number: 23

Cite as:  585 U. S. ____ (2018) 

19 

Opinion of the Court 

justiciable  controversy.    But  the  question  at  this  point  is
whether  the  plaintiffs  have  established  injury  in  fact.
That turns on effect, not intent, and requires a showing of
a  burden  on  the  plaintiffs’  votes  that  is  “actual  or  immi­
nent,  not  ‘conjectural’  or  ‘hypothetical.’ ”    Defenders  of 
Wildlife, 504 U. S., at 560. 

Third,  the  plaintiffs  offered  evidence  concerning  the
impact  that  Act  43  had  in  skewing  Wisconsin’s  statewide 
political  map  in  favor  of  Republicans.    This  evidence, 
which  made  up  the  heart  of  the  plaintiffs’  case,  was  de­
rived  from  partisan-asymmetry  studies  similar  to  those 
discussed  in  LULAC.  The  plaintiffs  contend  that  these
studies  measure  deviations  from  “partisan  symmetry,” 
which  they  describe  as  the  “social  scientific  tenet  that
[districting]  maps  should  treat  parties  symmetrically.”
Brief for Appellees 37.  In the District Court, the plaintiffs’ 
case  rested  largely  on  a  particular  measure  of  partisan
asymmetry—the  “efficiency  gap”  of  wasted  votes.    See 
supra,  at  3–4.    That  measure  was  first  developed  in  two 
academic articles published shortly before the initiation of
this  lawsuit.  See  Stephanopoulos  &  McGhee,  Partisan
Gerrymandering  and  the  Efficiency  Gap,  82  U.  Chi. 
L. Rev.  831  (2015);  McGhee,  Measuring  Partisan  Bias  in
Single-Member District Electoral Systems, 39 Leg. Studies
Q. 55 (2014).

The plaintiffs asserted in their complaint that the “effi­
ciency  gap  captures  in  a  single  number  all  of  a  district 
plan’s cracking and packing.”  1 App. 28–29, Complaint ¶5 
(emphasis  deleted).    That  number  is  calculated  by  sub­
tracting  the  statewide  sum  of  one  party’s  wasted  votes
from  the  statewide  sum  of  the  other  party’s  wasted  votes 
and  dividing  the  result  by  the  statewide  sum  of  all  votes 
cast, where “wasted votes” are defined as all votes cast for 
a  losing  candidate  and  all  votes cast  for  a  winning  candi­
date  beyond  the  50%  plus  one  that  ensures  victory.    See 
Brief for Eric McGhee as Amicus Curiae 6, and n. 3.  The