As votes are counted in the critical presidential swing state of Arizona, two key questions loom large: How many votes are left to count, and how many of those remaining votes does Vice President Kamala Harris or former President Donald J. Trump need to win the election?

The Arizona Republic/azcentral.com has built the above tool to help forecast answers for both.

The Republic's ballot tracker shows you an estimate of how many of the remaining votes a candidate must receive to win. It's updated every time the Arizona Secretary of State's Office releases new election results, and it shows how many ballots are counted so far.

The figure labeled "Projected Total Ballots" is not precise -- it is a rounded, forecasted estimate that reflects what historical election data tell us. The Republic projected this figure by modeling and analyzing that data.

When every county across the state releases estimates of ballots that remain uncounted, the figure labeled "Projected Total Ballots" will reflect an estimate based on those figures. That typically occurs in the day or days after the primary election.

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How we did it: Modeling the 2024 presidential election

Data reporters from The Republic worked with Christopher Weber, director of The Arizona Voter Project at the University of Arizona, to model turnout for the presidential election. Weber holds a doctorate in political science and has a background in statistics.

Reporters used a combination of five approaches -- from the simple to the complex -- to generate predictions, then averaged across them to create the rounded election turnout projection of approximately 3,370,000 total voters.

With Weber's guidance, a reporter used data collected by L2, a research company that combines voter registration information from the Arizona Secretary of State's Office with demographic information on registered voters across the nation, to perform several regression analyses. The statistical methods allowed us to better understand the relationship between voting in presidential general elections and factors like an individual's age, voting history and party affiliation.

All this to say: The Republic's estimate is a projection informed by historical data.

Our figure, which is above the leftmost bar in the chart above, is rounded down to the nearest 10,000th vote, and will be replaced by a projection informed by county estimates of remaining ballots when all counties report those figures.