How Numbers Drive Behavioral Decision-making

Numbers may influence our decisions more than we

think, according to new Wharton research.

Hospital patients rate their pain on a scale of one to 10. Teachers grade on a curve. And sports fans spend hours debating stats on their favorite teams. Even the most ardent language lover cannot deny the power of numbers to convey information, especially when choices need to be made. A new study from Wharton finds that people have a strong preference for numbers over words or graphical representations of the same information in decision-making — a phenomenon that researchers call “quantification fixation.”

Across 21 experiments, quantitative attributes consistently crowded out qualitative ones like star ratings, bar charts, and verbal descriptions when participants were asked to make comparative judgments on everything from planning a vacation to picking a job candidate. The results indicate a natural bias toward numbers that can have repercussions for decision-making in management, policy, consumer behavior, personal finance, and other vital topics.

“We know from this research that quantification isn’t neutral. When we count, we actually change what counts in people’s minds,” said Linda Chang, former MindCORE post-doctoral research fellow in Wharton’s Department of Operations, Information and Decisions (OID).

Chang was the lead author of the paper, “Does Counting Change What Counts? Quantification Fixation Biases Decision-making,” which was published last month in the journal Proceedings of the National Academy of Sciences (PNAS).

The paper was also co-authored by Wharton OID professor Katy Milkman; Erika Kirgios, behavioral science professor at the University of Chicago’s Booth School of Business and former Wharton PhD student; and Sendhil Mullainathan, a Massachusetts Institute of Technology professor who holds a joint appointment in MIT’s Electrical Engineering and Computer Science department and Economics department.

Chang said she’s not surprised by the influence numbers have on behavioral decision-making, but what stands out to her is the robustness of the effect, which was replicated across 21 experiments involving 23,000 randomly selected participants. Despite the significant sample size, the predilection for numbers never wavered, except when numbers were presented in ways that were harder to process. Chang and her co-authors describe the mechanism underlying quantification fixation as “comparison fluency,” or the ease of judging numerical values compared with non-numbers, such as words and pictures.

“Numbers are so fundamental to us. They are everywhere in the world,” she said. “Because they are ubiquitous in decision contexts, we are often comparing them. And our comparison fluency lulls us into looking at them and not at other representations,” she said.

How Do Numbers Affect Decision-making Behavior?

In one experiment, participants were asked to choose between making a $1 donation to The Nature Conservancy or The Natural Resources Defense Fund. Participants were provided with the nonprofits’ scores from Charity Navigator, an independent auditor, along two dimensions: (1) accountability and finance, and (2) culture and community.

The Natural Resources Defense Fund had a higher accountability and finance score, but a lower culture and community score; The Nature Conservancy had a lower accountability and finance score, but a higher culture and community score. Although participants always saw both scores for each charity, the researchers varied which score was presented numerically and which was presented as a bar graph. Participants donated more often to whichever charity dominated on the dimension quantified — for example, The Natural Resources Defense Fund received more donations when the accountability and finance score was represented as a number than when it wasn’t. This experiment (and many others involving different comparisons) was replicated with different participant populations, and the results were the same.

“After running roughly two dozen studies that showed quantification fixation in setting after setting, I have accepted that quantified information really dominates other kinds of information when we’re making trade-offs,” Milkman said. “At least, that’s what we’re seeing in our culture where numbers are so ever-present that people are used to seeing everything from their neighborhood restaurant to their newborn baby’s health given a numeric score.”

Milkman has done previous research on nudges that shows how language can move people to take up positive behaviors, such as exercising or getting vaccinated. She said that quantification fixation doesn’t contradict the power of a compelling story, but quantifying a feature can help sell the narrative.

“If you really want to change someone’s mind, and that person is making trade-offs, you might be best off telling a persuasive story that’s combined with sharing an impressive score,” she said. “If I want to convince you to donate to my charity, I’d still tell you an emotional story about a specific family that benefitted from our work and the plight we helped that family overcome. But then I’d let you know that Charity Navigator rated us a 99 out of 100 on their impact scale, which is, by the way, higher than the 97 they gave to the other local nonprofit you were considering.”

Beware of Decision-making Biases

Milkman also cautioned that quantification fixation can backfire. When comparing entities that are closely scored — like choosing between two five-star restaurants or two intern candidates with a very similar grade point average — non-numerical factors should often drive our decisions but may be inappropriately under-valued.

“The next time you’re picking a banana bread recipe on your favorite website, don’t pick the one that gets a 4.8 over the one that gets a 4.7 without giving its other attributes much thought,” she said. “If the 4.8 contains nuts and you aren’t a fan, remind yourself that you might be over-weighting the 4.8 rating and under-appreciating the value of ingredients that match your tastes.”

Chang said the study points to the importance of how choices are crafted and presented, especially when people are making consequential decisions about their lives — like taking one job offer versus another, one mortgage versus another, or picking one political candidate versus another. In her new job as an applied behavioral scientist at Toyota Research Institute, she works on understanding how and when people decide to adopt carbon-neutral behaviors and technologies, which may be another context where the role of quantification is crucial.

“There’s a real responsibility in thinking about how quantifying some information and not other information can systematically change people’s decisions,” she said. “There are implications for how people and organizations direct their time, attention, and resources.”