Nothing’s certain, but Arizona likely to gain 10th congressional district

Arizona has gained an additional congressional district every decade since 1960. The state even gained two districts, going from six to eight, after the 2000 U.S. Census.

Will Arizona gain its 10th district when the 2020 Census results are tabulated? We won’t know for sure until January 2021, but the trend looks promising.

Every December, after the U.S. Census Bureau publishes estimates of state populations, I calculate each state’s allocation of seats in Congress, using the “method of equal proportions” reapportionment formula adopted and used by Congress since 1941.

My analysis method tracks the year-by-year change in each state’s seat allocation priority, plotting a trend line, or ‘trajectory’ for each seat. The trend lines for existing seats and potential new seats I graph in relation to line representing the 435th seat, which is the maximum number of seats in the U.S. House of Representatives.

Once a state’s seat is ranked 435th or lower, that seat is awarded to the state after the next decennial census. If a current seat becomes ranked 436th or higher, the state will lose the seat. There is no specific population figure that guarantees a new seat. Each state’s eligibility to gain or lose is completely dependent on the formula’s simultaneous ‘pushing and pulling’ of populations in the other 49 states.

In 2017, Arizona’s 10th seat trend line had an ‘eligibility priority’ value of 440, five points above the 435th seat ceiling. But a year later, the priority value was 432 – eligible with three points to spare. This year, the 10th seat priority value is 431 – eligible with four points to spare. But the deceleration of the trend line is worrying. If Arizona wants a 10th seat, households must respond to the 2020 Census.

According to data from the U.S. Census Bureau, Arizona has gained about 886,000 residents since 2010, giving the state an estimated population of nearly 7.3 million. Since the last census, Arizona has gained more people than all but six states: California, Florida, Georgia, North Carolina, Texas and Washington.

Arizona gained more than 120,000 new residents in 2019, according to the Census Bureau. Only Florida and Texas saw more total population growth during that year.

If Arizona gains a seat, who loses one? Considering where each state’s trend line will be in 2020, I predict:

— Single-seat losses in California, Illinois, Michigan, Ohio, Pennsylvania, Rhode Island, and West Virginia.

— A two-seat loss in New York.

— Single-seat gains in Arizona, Colorado, Montana, North Carolina, and Oregon.

— Two-seat gains in Florida and Texas.

Yes, California looks like it might lose the 53rd District it picked up after the 2000 Census.