The length of a Black Friday checkout line affects how much you buy, according to science

Customers wait in line to enter a Walmart on Thanksgiving Day in Troy, Michigan.
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Waiting in lines is a ceremonial part of Black Friday. Even with almost half, or 46%, of shoppers planning to exclusively shop online, according to data from Decluttr, stories of people camping outside their favorite store on Thanksgiving night still dot the internet.

Despite past studies that estimate retailers can lose billions due to long checkout lines, a recent Georgetown University study by business professors John Cui and Sezer Ulku actually found the opposite. The longer the line, the more money you're likely to spend.

The mental traps that can lead you to spend more

Cui and Ulku study the effect of lines on how much we buy, something they call "purchase intention." They attribute shoppers' line-influenced behavior to two mental traps known as sunk cost fallacy and cognitive dissonance.

The sunk cost fallacy is when you continue a behavior because of a previous investment. For example, if you order too much food at a restaurant, you may force yourself to eat everything to "get your money's worth." That money is already gone, though, and your eating more or less doesn't change that.

Cognitive dissonance refers to the feeling of discomfort when your beliefs and behaviors don't align. For example, if you think consuming beef is bad for the environment but love to eat burgers, you may experience some cognitive dissonance.

How cognitive bias affects your investments

Video by Courtney Stith

Your purchase intentions are due to a marriage of these two phenomenons, the professors found. For the study, they recorded purchase intentions of shoppers in six different queues including a line for a salad restaurant and a line for a cupcake shop. In all lines, they found that purchasing intention increased with the length of the line.

"You wait for one hour, now you have wasted all this time, and if you end up buying something small, you may feel like it wasn't worth it so, as a result, you may adjust your purchase behavior," Ulku says. "You experience mental discomfort so you change behavior to reduce this discomfort."

How 'purchase intention' can cost you on Black Friday

Cui's own Black Friday experience led him to study purchase intention. When he was a 20-something grad student at the University of Pennsylvania, he and his wife waited outside a handbag store on Black Friday for four hours. By the time the two were finally let in, "everything good was gone, anything you would want to buy was gone," he says.

But that didn't stop them from making a purchase. "Because we had waited so long, my wife decided to buy a product just to justify the long wait we had suffered," he says. "And in the end, she didn't use that product at all."

Because we had waited so long, my wife decided to buy a product just to justify the long wait we had suffered. And in the end she didn't use that product at all.
Dr. John Cui
Professor at Georgetown University

You don't have to suffer the same fate.

Cognitive dissonance depends on you feeling uncomfortable. So, theoretically, the less agitated you are while waiting on Black Friday, the less you may feel the need to buy.

In their study, Cui and Ulku found that people who were distracted by a video felt less pain while waiting and therefore didn't buy as much, though they still bought more than those who didn't have to wait in any line. Distracting yourself with a book or a downloaded movie could relieve some of the discomfort of waiting.

A Black Friday line is can also be less painful than other shopping lines because it is an event in itself. You're usually shoulder to shoulder with fellow intense shoppers, or perhaps it's a tradition for your family members to rush the doors of Best Buy at 4 a.m. together. All of these exciting emotions, Cui and Ulku say, could lower your purchase intentions and help you resist the need to buy more to justify your time in line.

Regardless, Cui says, the emotions around Black Friday do make purchase intentions hard to predict. "If you're happier, according to our theory, you end up buying less," he says. "But because you're happier, you're more likely to make impulsive purchases. If you enjoy the Black Friday atmosphere, it could be very likely you end up buying more."

So if you're planning on waiting in line on Black Friday, you may want to go armed with something to entertain you while you wait — and a detailed shopping list to help you keep an eye on your budget and stay on track.

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