Stars or numbers? How rating formats change consumer behavior

In six experiments, the researchers found that consumers tend to overestimate fractional star ratings and underestimate fractional numerals. In either case, the ratings can be misleading, potentially causing a company to unknowingly overpromise and underdeliver -- or sell its own product short.

"Overestimating Stars, Underestimating Numbers: The Hidden Impact of Rating Formats," was published May 15 in the Journal of Marketing Research.

"When these pictures communicate a fractional number -- say 3.5, where there are three full stars and one-half star -- our brain automatically completes this half picture," said first author Deepak Sirwani, now an assistant professor in the Marketing and Behavioural Science Division at the University of British Columbia. "But when the same rating is communicated using numbers, we focus on the left digit, which is '3,' and that's why 3.5 feels more like a 3 than a 4. That's why we underestimate it."

According to Manoj Thomas, a professor of management at Cornell University, this work is really about the human brain and how it processes images and standard Arabic numerals.

"Our results suggest that the brain representations that are activated when you process stars are completely different from the brain representations that are activated when you process Arabic numerals. That realization was the a-ha! moment," Thomas said. "Most people don't realize that, but it's a huge difference."

The researchers found consistent results across all six experiments they ran. In study 1, for example, they sought to measure the perceived accuracy of ratings using stars versus numerals. A total of 616 participants were randomly assigned to one of three experiment conditions based on the type of rating symbol used: stars; numerals; or both.

Participants were presented with 17 numeric ratings, from 1 to 5, in increments of 0.25, one at a time and in random order, and were asked to estimate the position of each rating on an unmarked horizontal line, with endpoints 1 and 5.

The participants consistently overestimated the magnitude of fractional star ratings while underestimating the magnitude of the numeric ratings.

The group said their findings demonstrate that prevalent rating formats are misleading, highlighting the need for new industry standards.

"What makes this research powerful is the importance of ratings in the current marketplace," Sirwani said. "Most of us do not buy anything without checking its rating nowadays, and rating has become as powerful a predictor of purchase as price, or brand or even recommendations from friends and family."

Other research, he said, has indicated that even a rating jump of 0.2 points can increase sales by up to 300%. "We are showing," he said, "that sales could potentially increase by orders of magnitude by just showing stars instead of numbers."