As the holidays approach, we’ll all experience the temptation to overspend on gifts for our loved ones (and maybe a little on ourselves). When faced with difficult decisions like whether to spend $199 on a knife set or a tool set, we may follow the age-old advice “sleep on it.”
It just makes sense that waking fresh and clearheaded makes us better able to see decisions in a clearer light.
That’s certainly what Uma R. Karmarkar, an assistant professor in the Marketing unit at Harvard Business School, thought going into a string of experiments to test how sleep affects decision making. After all, sleep can do many things—research has shown that a good eight hours of shut-eye can help make people more creative, more attentive, less risky in their behaviors, and less driven by their emotions.
“There is reason to believe that with all of these positive cognitive effects, you might also get benefits for decision making,” says Karmarkar, who conducted the research with UMass Amherst psychology professor Rebecca Spencer and Stanford Graduate School of Business marketing professor Baba Shiv. “We hypothesized that people should feel more confident about their decision making after sleep.”
What they actually found was just the opposite. Sleep makes them feel better in some ways but does not boost confidence in their ability to make the best decision. They published their findings in the paper Should You Sleep On It? The Effects of Overnight Sleep on Subjective Preference-Based Choice, forthcoming in the Journal of Behavioral Decision Making.
In order to test their supposition, Karmarkar and her co-researchers conducted an experiment in which they showed a group of graduate students four laptop bags and had them choose which one they liked the best. All four bags were similar—same price, same color, generally the same quality—but each had different features.
Along with the bags themselves, the researchers showed the students positive or negative information about the bags, such as “has a sturdy zipper” or “not large enough for a 17” laptop,” and asked them to remember as many of the attributes as they could. As a final addition, the students were told they would have a 1 in 25 chance of winning a raffle to receive their chosen bag, to give them some skin in the game and make them more serious about their choice.
Then, the students were excused for 12 hours. Some did the initial selection of a bag at night and were told to come back in the morning, after a night’s sleep; others performed the initial selection in the morning and were told to come back in the evening.
At no point were they told that the experiment was about sleep—but that’s exactly what the researchers were trying to test. Past psychological research has shown that sleep benefits memory through a process known as “sleep-dependent consolidation.”
“The idea is that when you sleep you stabilize the information you’ve learned,” says Karmarkar. “It’s somewhat like moving information from short-term to long-term storage.” It’s as if you are saving a Word file to your hard drive, for example, or organizing a bunch of papers on your desk into neat files.
Karmarkar’s team theorized that sleep might aid decision making as well. “If sleep helps organize and store information, it could be doing so in a way that helps you make a better informed choice.”
UNSURE OF THE DECISION
The researchers conducted two studies, one in which they listed 6 positive and 3 negative attributes for each bag; and one in which they listed 4 positive and 4 negative attributes for each bag (for a total of 36 and 24 attributes, respectively, for the four bags). In each study, those who slept remembered on average slightly more attributes—13.17 versus 12.84 attributes in the first study and 13.22 versus 11.95 attributes in the second. (Students who said they had napped during the day were excluded.)
Interestingly, if participants slept on the decision, they tended to remember more positive attributes about all the bags, not just the one they had chosen—as if with the light of morning, they saw the decision more favorably overall. (This ﬁnding contrasts with previous research showing that sleep selectively enhances recall for negative information.)
But there was a twist. When asked how confident they were that they had chosen the right bag, how satisfied they were with the choice, and how easy the decision was to make, those who had slept tended to be less certain with their choice in the first study, and about the same in the second.
In fact, sleeping on their decision seemed to make some participants less interested in actually spending money to buy the bag of their choice.
(The researchers also ran a third experiment to ensure that the results weren’t just due to the time of day the decision was made, finding little difference in how participants rated these kinds of choices in the morning versus the evening. So the effects did seem to depend on sleep, says Karmarkar.)
FEELING WORSE FROM SLEEPING ON IT
The findings led the research team to a surprising conclusion: “Nothing about sleeping on it makes you feel better [about the decision you made], and it might make you feel worse,” she says.
Karmarkar surmises that the new positivity gained after sleep may have made people less able to rule out some of the bags—making the decision harder, not easier.
She hastens to add that this study can’t tell you for sure whether people picked the “best” choice—since each of the laptop bags was about the same quality overall. It’s still possible that sleep might help individuals bring together information in a way that would cause them to make better choices when there is an objectively right answer—something that Karmarkar and her co-researchers hope to investigate in a future study.
However, for many situations, people just need to be able to select one thing from a few reasonable choices. Here, says Karmarkar, who holds Ph.D. degrees in neuroscience and marketing: “if you are trying to make people feel more confident and rule out options, there could be some benefit to stepping away for a period, but not necessarily sleeping on it.”
In other words, the next time you face a difficult decision, you might want to get some distance from it for a while—but make up your mind before bedtime.
Michael Blanding is a senior writer for Harvard Business School Working Knowledge.
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[This article was provided with permission from Harvard Business School Working Knowledge.]