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Nonpartisan Primaries

Nonpartisan Primaries Increase Primary Turnout

States with nonpartisan primaries see significant boosts in voter turnout, as shown by higher participation rates in Alaska, Washington, and California, with studies highlighting greater inclusivity and representation across diverse demographics.

Carlo Macomber
Research Manager
June 28, 2024

Topline Findings:

  • States that adopt nonpartisan primaries see a 6.1-percentage point increase in primary election turnout;
  • In 2022, primary turnout nationally was just 21%. But turnout in the three states with nonpartisan primaries — Alaska (37%), Washington (35%) and California (29%) — was much higher, according to the Bipartisan Policy Center.
  • A study that analyzed the impact of open primary systems on voters from different racial demographics found that all groups turn out at higher rates in more open systems. However, the increase in participation is larger among some communities of color, thus decreasing the turnout gap between white voters and voters of color.


Since the direct primary was adopted throughout the country in the early 1900s, the vast majority of states have held partisan primaries in which each party has a separate ballot that only lists its own candidates. Voters are only able to vote in one party’s primary, and, therefore, must only vote for candidates from that one party. In states with closed partisan primaries, voters not registered with a party (i.e., independents) are not able to participate in primaries at all.

In recent years, four states (Alaska, California, Louisiana, and Washington) have held nonpartisan primaries for state and congressional offices. In a nonpartisan primary, all candidates, regardless of their party affiliation (or lack thereof), run together on the same ballot. All eligible voters can participate and vote for any candidate from any party for each office — even if that means supporting a Republican for U.S. Senate, a Democrat for U.S. House, and an independent in the governor’s race. The top finishers, also regardless of party, advance to the general election. 

Studies have found that replacing partisan primaries with nonpartisan primaries leads to an increase in voter participation in primary elections. 

Why Nonpartisan Primaries Increase Turnout

There are several theoretical reasons that implementing nonpartisan primaries may increase voter turnout in primaries.

  • First, all eligible voters can participate. This means that any state with closed primaries could implement nonpartisan primaries and expect to see an increase in turnout as a result of the enfranchisement of independent voters. 
  • Second, nonpartisan primaries offer voters increased flexibility: All voters can vote for any candidates (including independents and minor party candidates) for each office. Voters who prefer a Republican for one office and a Democrat for another may be more likely to vote in a nonpartisan primary because it allows them to express their true preferences.
  • Third, nonpartisan primaries can encourage more ideologically and demographically representative candidates to seek office because they do not have to run in a partisan primary. The presence of these candidates can, in turn,  inspire non-voters — who dislike their options under the status quo — to participate in the primary. A recent study of non-voters found that the top reason they do not participate is because they do not like any of the candidates.
  • Fourth, more candidates tend to run in nonpartisan primaries, creating more competition and a greater incentive for voters to participate. Uncontested partisan primaries can serve as a deterrent to participation as voters do not see the point in incurring the costs to vote in an election with a predetermined outcome.

While it can be difficult to isolate the impact of a reform on turnout given that many unrelated factors — including the timing, competitiveness, and salience of the election — contribute to higher or lower participation rates, the findings summarized in the remainder of this explainer attempt to control for these extenuating circumstances.

Nonpartisan Primaries and Voter Turnout

In the last few years, several studies have analyzed the impact of nonpartisan primaries on turnout and concluded that the reform has a positive effect.

1. Scholar Seth Hill of the University of California San Diego found that in U.S. House primaries held between 1992-2014, states that adopted nonpartisan primaries saw a 6.1-percentage point increase in primary election turnout when controlling for other factors. some text

  1. He noted that the 6-point increase in turnout “is of political importance suggesting that nonpartisan primaries do serve the goal of increasing participation.” 
  2. On the whole, he concluded that his analysis “suggests easing restrictions on voting in primary elections increases participation in nominating contests, but uncertainty about the magnitude remains given sampling variability.”

2. A report from the Bipartisan Policy Center (BPC) that analyzed primary election turnout during the 2022 midterms found that states with nonpartisan primaries experience higher primary turnout than states with partisan primaries.some text

  1. Nationwide, primary election turnout was 21.3% of eligible voters in 2022. But in Alaska, the only state with a top-four nonpartisan primary, 37% of eligible voters turned out for the primary. In Washington and California, two states with top-two nonpartisan primaries, primary turnout was 35% and 29%, respectively. On average, states with closed partisan primaries experienced primary turnout below 20% on average.
  2. The BPC researchers also conducted regression analyses that controlled for state and year and concluded that a state that switches from a closed primary to a nonpartisan primary can boost primary turnout by three percentage points. They also found a smaller effect of two percentage points for states that switch from a closed primary to a more open partisan primary system.

3. A group of scholars from the University of Southern California studied the impact of different primary systems on the turnout rates of independent voters of color. They found that: “Open and top-two primaries are associated with higher turnout from independent voters of color in both primary and general elections,” suggesting that more open primaries can also have a downstream effect on general election turnout. some text

  1. The authors analyze validated survey data from 2012-2018 and find that Asian American and Latino voters from closed primary states are more likely than white voters to be registered independents, indicating that they are disproportionately impacted by restrictive primary participation rules. About 25% of Asian American and Latino voters from closed primary states are registered independents, compared to 18% of white voters.
  2. They also found that in more open primary systems, Black independents participate at rates on par with white independents in both the primary and general elections. This is not true in closed systems.
  3. There are downstream turnout effects to opening up primaries: The probability that Latino independents from closed primary states will turn out to vote in a general election is just 20%. This probability doubles to 40% for Latino independents from open primary states. For Black independents, the probability more than doubles from 20% to 49%.
  4. Overall, the paper concludes: “Open and top-two primaries increase [primary] turnout for people of color — and also increase turnout for whites.”

Since only four states have nonpartisan primaries, this evidence can be considered preliminary. Nevertheless, all findings point in the same direction: Primary election turnout increases when states implement nonpartisan primaries. As more states adopt nonpartisan primaries, more data points will be available, and the evidence of the reform’s impact on turnout will likely become stronger.