Wharton operations and information management professor Katherine Milkman loves to read about and listen to audiobooks on almost any topic, from behavioral economics to historical biographies. But she has a weak spot for addictive fiction novels like The Hunger Games. So a few years ago, when she was having trouble making it to the gym on a regular basis, she decided to allow herself to enjoy these less-than-scholarly audiobooks only when she was exercising. The result: Milkman began hitting the gym five days a week.

Fast forward five years, and Milkman decided to see if her experience restricting her more escapist reads to exercise time could be developed into an intervention capable of helping others with similar self-control struggles. In her research, she coined a new concept: temptation bundling, “which involves coupling instantly gratifying ‘want’ activities with engagement in a ‘should behavior’ that provides long-term benefits but requires the exertion of willpower,” according to one of her recent papers.

“I was employing temptation bundling long before I named it,” Milkman says. “It was just another way to solve a self-control problem.”

Along with Wharton health care management professor Kevin Volpp and Harvard Kennedy School professor Julia Minson (formerly a Wharton post-doctoral scholar), Milkman evaluates the effectiveness of temptation bundling — and whether or not people would pay for these restrictive bundles — in the paper, “Holding the Hunger Games Hostage at the Gym: An Evaluation of Temptation Bundling.”

“I was employing temptation bundling long before I named it. It was just another way to solve a self-control problem.” –Katherine Milkman

Their theory: “Valuable healthy behaviors could be increased, while guilt and wasted time from indulgent behaviors decreased, through the use of temptation bundling.” And while the concept and term temptation bundling has never been analyzed before, the researchers note, the research does relate to studies of commitment devices — i.e., people putting their own money on the line and agreeing to forfeit it if they fail to achieve their goals in order to encourage “should” behaviors like exercise — which other research has suggested can be effective.

The nine-week temptation bundling study looked at 226 students and faculty who belonged to a university gym, all of whom indicated they wanted to work out more. Participants were divided into three groups: One got iPods loaded with four tempting novels of their choice, but were only allowed to access them at the gym. Those who were part of the second group received the same audiobooks but loaded them on their own iPods and could thus take them home, although they were encouraged to only listen to the devices at the gym. Members of the third group (a control group) were each given a $25 gift card (valued equivalently by this population to the loan of four audiobooks) and were simply encouraged to work out more. The participants selected from 82 pre-tested novels deemed highly tempting, including The Hunger Games trilogy, The Da Vinci Code, the Twilight series and The Help.

Initially, the researchers found that those who had gym-only audiobook access attended the gym 51% more than the control group and 29% more than the group encouraged to self-restrict their enjoyment of tempting audio-novels to the gym. The effects weakened somewhat over time, however, with Thanksgiving break arriving in the eighth week of the nine-week study and causing a precipitous drop in gym attendance for all groups. “We find that attendance rates increased meaningfully and significantly with access to the temptation bundling program, suggesting that temptation bundling creates value,” the paper states.

According to Milkman, the iPods were most effective for those who had the busiest schedules (measured based on participants’ availability to meet with researchers at the outset of the study). The busiest people with gym-only iPod access boosted their gym attendance by an extra 0.21 visits per week above and beyond the 0.46 visit per week initial benefit experienced by average participants in the same group. “I thought it was really cool that the busiest people got the most out of it,” Milkman notes. “But it makes sense that they especially need that extra push to go to the gym.”

When the study ended, participants were entered in a lottery to win an iPod loaded with audiobooks. If they won the iPod, they were asked if they would like to pay the researchers to take this iPod away from them and ensure it could only be accessed at the gym. Much to the surprise of the researchers, 61% of the study participants (from all of the experimental groups) were willing to pay for this restriction on a possession they could otherwise access freely, at an average price of $6.91.

“It’s very interesting, as standard economics would suggest that nobody would pay to have their options constrained,” Volpp points out. “The willingness to pay tells us that people recognize that this device is something that has value.” One possible explanation, Minson adds, could be that “some people are savvy enough to appreciate they need restrictions, but not savvy enough to restrict themselves, so they would pay someone else to do it.”

A Realm of Possibility

This willingness to pay, according to Milkman, opens up a whole realm of possibility for mass-marketed commercial devices. She envisions some sort of mobile app that works with a phone’s geo-location tracking, allowing people to access certain audiobooks or music only when they are at a specific location, like the gym. Or it could be an account fashioned in the vein of Netflix that allows consumers to set aside to a subset of their favorite movies and television shows for gym-only access (or access only through the TVs connected to exercise equipment).

“It’s very interesting, as standard economics would suggest that nobody would pay to have their options constrained. The willingness to pay tells us that people recognize this device is something that has value.” –Kevin Volpp

Milkman adds that temptation bundling can be applied in a variety of ways outside of the gym. For example, imagine you crave unhealthy food (e.g., cheeseburgers or cream-filled donuts) and have a difficult uncle whom you know you should spend more time with. You can prevent overindulging and increase time spent with that cranky uncle by allowing yourself to eat your favorite food only when bonding with him. Or if you tend to overindulge in pedicures or spend too much time lingering over $5 lattes at a coffee shop and struggle to complete tedious work assignments, you could only treat yourself to pedicures or lattes when working on dreaded assignments. “Temptation bundling can simultaneously solve two problems at once in many different situations,” Milkman says.

Before unleashing temptation bundling on the larger population, however, Milkman and her colleagues agree that further research needs to be done on the topic. The most important questions, according to Milkman, include how to sustain the initial benefits found from restricting access to the iPods and how to re-engage people with tempting content after time away from the gym since the initial benefits of temptation bundling in this gym experiment wore off after participants left campus for Thanksgiving break.

Volpp adds that further research could also look at how employers and insurers can use temptation bundling as a way to encourage healthier living. “It’s a highly promising concept, but it’s not ready for prime time and large-scale application yet.”

To watch a short video about temptation bundling, click here.