For generations, the standard way to learn how to ride a bicycle was with training wheels or a tricycle. But in recent years, many parents have opted to train their kids with balance bikes, pedalless two-wheelers that enable children to develop the coordination needed for bicycling—a skill that is not as easily acquired with an extra set of wheels.
Given the benefits of balance bikes, why did it take so long for them to replace training wheels? There are plenty of other examples in which overlooked solutions that involve subtraction turn out to be better alternatives. In some European cities, for example, urban planners have gotten rid of traffic lights and road signs to make streets safer—an idea that runs counter to conventional traffic design.
Leidy Klotz, an engineer at the University of Virginia, noticed that minimalist designs, in which elements are removed from an existing model, were uncommon. So he reached out to Gabrielle Adams, a social psychologist at the university, to try to figure out why this was the case. The two researchers hypothesized that there might be a psychological explanation: when faced with a problem, people tend to select solutions that involve adding new elements rather than taking existing components away.
Adams, Klotz and their colleagues set out to test if their hunch was correct. “We wanted to investigate whether, and to what extent, people actually overlooked subtraction when they’re tasked with changing things,” Adams says. Their investigation “wasn’t literature driven, because there’s [no academic] literature on this phenomenon. It was really just us putting our heads together to think up why this might be the case.”
The researchers first carried out a set of observational studies, assessments without a control group, to see whether this bias existed at all. In one, they asked 91 participants to make a pattern symmetrical by either adding or removing colored boxes. Only 18 people (20 percent) used subtraction. In another, the team scanned through an archive of ideas for improvement submitted to an incoming university president and found that only 11 percent of 651 proposals involved eliminating an existing regulation, practice or program. Similar results emerged across tasks that involved modifying structures, essays and itineraries—in each case, the vast majority of people chose to augment rather than remove.
To determine why people tended to choose additive solutions, the team dug deeper by conducting a series of eight experiments with more than 1,500 individuals recruited either from a university campus or through Amazon Mechanical Turk, a crowdsourcing Web site. In one experiment, people were asked to stabilize the roof of a Lego structure held up by a single block that rested atop a cube-shaped base. The reward for completing the task was $1, and participants could add new blocks for 10 cents apiece or get rid of blocks for free. The researchers wrote that one group was provided a cue about potential subtractive solutions by being told, “Each piece that you add costs ten cents but removing pieces is free,” while another group was just told, “Each piece that you add costs ten cents.” Almost two thirds of people in the cued group ended up choosing to eliminate the single block rather than adding new ones, compared with 41 percent of those who had not received the prompt.
The researchers also observed that people were more likely to remove features when they were given more opportunities to consider alternative ways to address a problem: when participants were asked to create a symmetrical pattern by adding or eliminating colored blocks, they opted for removal more often if they were given practice trials than if they had just one chance to tackle the problem. On the other hand, having to simultaneously juggle another task—such as keeping track of numbers on a screen—made individuals less likely to subtract elements to solve the same problem, suggesting that it requires more effort to think up subtractive solutions than additive ones. (In both of these experiments, removing blocks was the more efficient solution.)
These findings, which were published today in Nature, suggest that “additive solutions have sort of a privileged status—they tend to come to mind quickly and easily,” says Benjamin Converse, a social psychologist at the University of Virginia and a co-author of the study. “Subtractive solutions are not necessarily harder to consider, but they take more effort to find.”
The authors “convincingly demonstrate that we tend to not consider subtractive solutions as much as additive ones,” says Tom Meyvis, a consumer psychologist at New York University, who was not directly involved in the study but reviewed it and co-authored a commentary about it in Nature. While the propensity for businesses and organizations to opt for complexity rather than simplification was previously known, the novelty of this paper is that it shows that people tend toward adding new features, “even when subtracting would clearly be better,” he adds. Meyvis also notes that other reasons for this effect may be a greater likelihood that additive solutions will be appreciated or the so-called sunk-cost bias, in which people continue investing in things for which time, money or effort has already been spent.
A number of open questions remain, such as whether the bias against subtractive solutions generalizes across cultures and if it exists in childhood or develops over time. For now the team hopes that these findings will encourage people across various fields, whether they be engineering, architecture or medicine, to think about subtractive options—such as balance bikes—that might be typically be overlooked. “The hope is that, just by getting people to think about this more, that maybe it will help inspire some other neglected subtractions,” Converse says.