When Maryland began redrawing its congressional district lines after the 2010 census, its 6th district needed to lose fewer than 20,000 people to satisfy population equality requirements. But the Maryland legislature moved more than 40 times the required number — 700,000 people — into and out of the district. The Maryland map was part of a 2019 Supreme Court case involving accusations of partisan gerrymandering, and we wondered then if this extreme population shift was an indicator of partisan gerrymandering. We now understand that it indeed plays a significant role in the increase in population shifts. Who draws the maps also matters.
In an article published in Election Law Journal, we examine the population shifts between any two districts in each state over the six redistricting cycles since the 1970 census. We control for political factors like which party is in power when districts are redrawn and whether a court or commission drew the maps instead of the legislature. We also control for changes in the number of districts in each state after House seats are apportioned among the states. We use the partisan gerrymandering test in the Freedom to Vote Act to identify plans that would trigger the rebuttable presumption of partisan bias.
Our first objective was to understand how population shifts have changed over these six redistricting cycles and whether the extreme instance of the 6th district in Maryland is becoming more common over time. We found evidence that is the case.
In 1970, the ratio of actual population shifts to the minimum needed to reach population balance in the median district was 2.8. In other words, if a district needed to move only 1 person to reach population balance, almost 3 people were moved. By 1990, this ratio increased dramatically to 8.1. That means more than 8 people are now moved between districts when only 1 is required. This ratio declined to 7.5 in 2000 but ramped up again in 2010 to about 8.6. In 2020, the ratio was 9.4. Thus, the severity of population shifts in redistricting has more than tripled since the 1970s.
Our second objective was to understand under what circumstances these population shifts were larger or smaller and how districts held by the party in charge of the process were treated. Perhaps unsurprisingly, House districts held by the same party in charge of the process were kept together to a greater extent than seats held by the other party. Evidence shows “out-party” seats are fragmented to a greater degree than other seats, suggesting that redistricting is used to make reelection more difficult for the party not in charge of drawing districts. Maps we identify as partisan gerrymanders also exhibit a higher degree of fragmentation than other districts.
Some states have experimented with commissions drawing districts, rather than the state legislature, in order to break up the inherent conflict of interest when legislators are drawing congressional districts. A fascinating pattern emerged: Appointed commissions, like in New Jersey and Washington, tend to draw districts that minimize changes over time, meaning districts tend to look the same before and after the census is conducted. Independent commissions, on the other hand, fragment districts to a higher degree than appointed commissions. That result is likely due to independent commissions taking a completely different approach to drawing districts. One of the members of the newly created California commission summarized their work as, “It really should have been called ‘districting’ because the commission consciously chose not to tweak existing districts with their flawed political baggage, but to start from scratch using its constitutionally approved criteria.”
Another pattern emerged when comparing the degree of district fragmentation in partisan gerrymanders drawn by a legislature to plans drawn by independent commissions. Fragmentation is lower among commission-drawn plans when there is a change in the number of House seats in a state — the fragmentation in the commission plans is a result of needing to add or remove a district from the state. Legislative-drawn plans, on the other hand, fragment districts at roughly the same rate regardless of a change in the number of districts. Furthermore, when we look at the districts drawn after the Supreme Court’s 2019 ruling that federal courts cannot review partisan gerrymandering challenges, district fragmentation is higher in partisan gerrymandered maps when compared to maps drawn by independent commissions.
Our research shows redistricting has become more expansive and excessive over time in terms of the people displaced from their congressional district. Partisan gerrymandering plays a significant role in the growth in these population shifts. The solution, however, is not to limit population shifts but rather to change who holds the pen from conflicted legislatures to impartial and independent commissions.
