Huntington–Hill method

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The Huntington–Hill method of apportionment assigns seats by finding a modified divisor D such that each constituency's priority quotient (population divided by D ), using the geometric mean of the lower and upper quota for the divisor, yields the correct number of seats that minimizes the percentage differences in the size of the congressional districts.[1] When envisioned as a proportional electoral system, this is effectively a highest averages method in which the divisors are given by , n being the number of seats a state is currently allocated in the apportionment process (the lower quota) and n+1 is the number of seats the state would have if it is assigned to this state (the upper quota).

The United States House of Representatives uses this method of apportionment to assign the number of representative seats to each state.

The method is credited to Edward Vermilye Huntington and Joseph Adna Hill.[2]


The formula for determining the priority of a state to be apportioned the next available seat defined by the method of equal proportions is

where P is the population of the state, and n is the number of seats it currently holds before the possible allocation of the next seat. An equivalent, recursive definition is

where n is still the number of seats the state has before allocation of the next, and for n = 1, the initial A1 is explicitly defined as


The U.S. House of Representatives guarantees one seat for each state. So, each state starts off with a divisor D of 1.41 (the square root of the product of 1, the number seats currently assigned, and 2, the number of seats that would next be assigned). Each state's census population is divided by its D, to produce a priority value for each state. Since all of the Ds are equal for this first seat, the state with the largest population would win (California).

Now, California's D would be changed to 2.45 (the square root of 2 × 3), and we would repeat this process. Unless California has about twice the population of any other state, the next largest state would win this second seat. In this case Texas would win the next seat because its population (24 million) divided by its current D (still 1.41) is greater than California's similarly calculated priority value (37 million ÷ 2.45) for priority values of 17 million and 15 million, respectively).

This process is repeated until all empty house seats have been exhausted. If the number of U.S. House of Representatives seats were equal in size to the population of the United States, this method would guarantee that the appointments would equal the populations of each state.

Although the U.S. House of Representatives currently uses the Equal Proportions method, Congress has not always used it. In fact, George Washington used the presidential veto power for the very first time in order to block apportionment legislation less favorable to his home state of Virginia. Had Congress used the Equal Proportionment Method (with a divisor of 34,800) to apportion House seats according to state population following the 1790 census, the 105 seats in the 3rd United States Congress the House of Representatives would have been apportioned as follows:

State Population Quotas Lower Upper G. Mean Rnd. Dir. Seats
Connecticut 236,841 6.81 6 7 6.48 up 7
Delaware 55,540 1.60 1 2 1.41 up 2
Georgia 70,835 2.04 2 3 2.45 down 2
Kentucky 68,705 1.97 1 2 1.41 up 2
Maryland 278,514 8.00 8 9 8.49 down 8
Massachusetts 475,327 13.66 13 14 13.49 up 14
New Hampshire 141,822 4.08 4 5 4.47 down 4
New Jersey 179,570 5.16 5 6 5.48 down 5
New York 331,589 9.53 9 10 9.49 up 10
North Carolina 353,523 10.16 10 11 10.49 down 10
Pennsylvania 432,879 12.44 12 13 12.49 down 12
Rhode Island 68,446 1.97 1 2 1.41 up 2
South Carolina 206,236 5.93 5 6 5.48 up 6
Vermont 85,533 2.46 2 3 2.45 up 3
Virginia 630,560 18.12 18 19 18.49 down 18

Compared with the actual apportionment, Pennsylvania and Virginia would have lost one seat each, while Delaware and Vermont would have gained one seat each.


  1. ^ "Congressional Apportionment". Retrieved 2009-02-14. 
  2. ^ "The History of Apportionment in America". American Mathematical Society. Retrieved 2009-02-15.