science of us

The Cognitive Bias That Makes You Bad at Online Shopping

Photo: Jim Young/Bloomberg via Getty Images

Last year, when I was in a bit of a rocker phase (don’t ask), I decided to buy a wristband online. After scrolling through options on Amazon, I found one I liked: a simple, black, ropelike bracelet that would match everything. The band’s rating wasn’t great — if I recall correctly, it had two or three stars — but it had more than a hundred reviews. And if so many people were buying it, I reasoned, could it really be that bad?

So I bought it, too, unaware that the strategy I’d just used to narrow down my options was actually a pretty bad one. In a new study recently published in Psychological Science, researchers discovered that product reviews might actually make it harder to choose quality products.

It all started when a group of scientists grew curious about how reviews affected online shopping. “We wanted to examine how people use this wealth of information when they make decisions, and specifically how they weigh information about other people’s decisions with information about the outcomes of those decisions,” Derek Powell, a researcher from Stanford University and the study’s lead author, explained in a statement.

After researching products on Amazon, the scientists found no connection between products that were bought more frequently and products that received high ratings — a finding that they then saw play out in real time when they recruited 132 volunteers to shop for phone cases online. The participants could see both average ratings and total ratings for each case, were heavily biased toward choosing products that had a lot of reviews, even if those reviews weren’t good. In other words, the study subjects seemed to be drawn toward popular products, regardless of whether that popularity was merited.

“It’s extremely common for websites and apps to display the average score of a product along with the number of reviews,” Powell explained. “Our research suggests that, in some cases, people might take this information and make systematically bad decisions with it.”

That sounds about right. When my wristband arrived in the mail, I was initially pretty pleased. It looked exactly like it did in the picture. But after a few days, the strings just fell apart. I realized that this must be exactly what happened to those other hundred-plus buyers. As I posted my own bad review on Amazon, I wondered if future customers would be smarter than I had been and actually read it. The evidence suggests that that probably wouldn’t be the case.

The Cognitive Bias That Makes You Bad at Online Shopping