The Science Behind How Your Vote Is Counted

How is your vote counted in an election year? How do voting machines work? And is voting really secure? Ask Science explains.

Sabrina Stierwalt, PhD
5-minute read
Episode #214

This week is a big one for us here in the US: we elect our president for the next four years. An estimated 129 million people voted in the 2012 presidential election, only about 55% of those eligible to do so. The process of how all of those votes are collected and then counted and the machinery we rely on to do it accurately are what the Verified Voting group call the “intersection of technology and democracy.”

We rely on voting machines and the design of the procedures performed by poll workers to safeguard this process and assure us that every vote counts. After all, you may disagree with some of the choices being made by elected officials or feel you are just one person trying to influence a large political machine, but in the US, you will always have your vote as a way of making your voice heard.

How Do Voting Machines Work?

In the 1800s, voting was done by voice. Voters showed up at a polling place, swore on the Bible that they were who they claimed to be and that they had not already voted, and then called out their choices. While voice voting allowed for independent tallies to be kept on the results, it also offered little protection against the influence of bribes or threats, forcing a person to vote a certain way.

There are still laws in place in many states that do not allow any photos taken in the voting booth to protect voters from being forced to offer proof of their choice. Now that we live in the selfie era, these laws are getting more attention, including in the 2016 election when Justin Timberlake posted a photo of himself casting his ballot in Tennessee. In case you’re hoping to memorialize your voting experience on social media, TIME magazine provided a map of which states allow voting selfies and which do not. Or maybe just play it safe and stick to just a photo with your “I voted” sticker.

The privacy of our voting practices have improved since the 1800s, but even after 56 presidential elections and 44 presidents, we continue a trial and error effort toward determining the best technology to use to count those votes.

The decision of what kind of voting machine to use is made at the state level, and paper ballots are still the dominant form of voting in the US. In the 2016 presidential election, ~3/4 of voters will cast their votes on a paper ballot. Once a voter fills in the circle or square next to their choice, an optical scanner will be used to record their ballot either at the polling site or once ballots from several polling sites are gathered in a more central location. The optical scanners can read as many as 10 ballots per second.

There are some jurisdictions where paper ballots are not scanned but instead counted by hand at the polling location. Most absentee ballots are conducted this way as well.

Some districts use Direct Recording Electronic systems (DREs) which collect a voter’s choices either through a touchscreen, push buttons, or a dial and then immediately stores the data to computer memory. Newer models are more likely to use touchscreens.  Some DREs have the option of printing a paper record which can act as an analog form of back up should a recount or an audit be necessary.

Some states employ a mix of paper ballots and DREs, and only five states, Delaware, Georgia, Louisiana, South Carolina, and New Jersey, use only DREs without the option for printing a paper record. Verified Voting has a map of what equipment is used in each state.

Punch cards voting machines (I think) will not be used in the 2016 election, and anyone who has been paying attention to the last several US elections will know why. In the 2000 presidential election between Bush and Gore, hundreds of ballots had to be discarded due to the issue of hanging chads, or holes that were not thoroughly punched. As a result, the Supreme Court had to be called upon to settle the final vote count.

This event is likely the inspiration for a significant fraction of the US population learning the phrase “hanging chad.” It also inspired the Help America Vote Act which passed in 2002 and worked to phase out the use of punch card voting machines.


Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.