It turns out that the key to happiness can be summed up in a single formula:
In plain English, it means that happiness depends on your expectations.
"Our basic finding is that happiness depends not on how well things are going, but whether things are going better or worse than expected," said study author Dr. Robb Rutledge, Senior Research Associate at the Max Planck UCL Centre for Computational Psychiatry and Ageing. "Our mathematical equation allows the influences of past rewards and expectations to be combined to predict how happy someone will be."
But, as might be expected, it's not that simple: Rutledge's equation can only calculate moment-to-moment happiness (as much as can be measured in a lab), and doesn't even begin to capture what most people care about when it comes to happiness -- life satisfaction.
"We can’t really change how satisfied people are with their lives in the lab — that doesn’t even make sense," said Rutledge in an interview with The Huffington Post. "But we can understand what determines happiness from moment to moment, and we do think that there’s some relationship between [momentary happiness and life satisfaction] that our research hasn’t examined yet."
Rutledge and team recruited 26 study participants and asked them to play a game in which they would either choose to earn a certain amount of money, or gamble with a chance to win or lose even more money. Every two or three games, researchers continually asked participants how happy they were at that moment.
After several games, the participants earned an average of £28.51-- quite a bit more than the initial £20 they earned just for showing up. But they reported more happiness per pound if the money they had won was a result of a gamble that turned out to exceed expectations.
Rutledge was able to confirm his equation by hooking up the lab participants to MRI machines. The brain scans showed a lot of activity in an area of the brain called the striatum, which is linked to reward and expectations.
"We measured brain activity in this area during the experiment, added it up using the equations, and then predicted how happy people will be at any point," explained Rutledge. "We’re hoping that this area of the brain might be the one that explains happiness, because it’s known to represent some of the variables in the equation."
Rutledge then wanted to see if the results from his lab experiments would hold in a more general population, so he designed a game included in the free smartphone app, "The Great Brain Experiment," that mimicked the gambling tasks he used on participants in the lab. Like the lab tasks, it incorporated questions about happiness every two to three games, but it didn't involve real money.
Rutledge was able to analyze 18,420 people who made over 200,000 happiness ratings playing his smartphone game, and he found that players made the same kinds of decisions and reported the same levels of happiness that participants made in his lab -- despite the fact that they weren't playing with real money.
"Their happiness depended on their previous decisions and the outcomes of those decisions, in exactly the same way as the lab," said Rutledge.
But before you resolve to permanently lower your expectations for everything, remember that we actually can get a pretty reliable low-grade buzz from high expectations. Consider the joy from booking airline tickets for a vacation, for example.
"You shouldn't have low expectations for your vacation, because you won't be able to enjoy the pleasant anticipation that comes from knowing something good is going to happen," Rutledge explained. The tradeoff comes, said Rutledge, if your expectations are so high that the trip ends up disappointing you in some way.
"In general, you want to have accurate expectations, because if you have accurate expectations you’ll make good decisions," Rutledge concluded.
Or say you want to use Rutledge's "equation" to make your family and friends happier. One way to do that, he said, is to tamp down on tendencies to hype an activity, experience or gift you're about to share with them. Imagine giving someone a wrapped present. As you hand it to them, try to resist the urge to say that they're "going to love it," or that the gift will "change their life."
"If you’ve just handed it to them, there’s no way they’re going to be happier in the end," said Rutledge. "They won’t be able to anticipate it for more than two seconds, and then they’re more likely to be disappointed because you’ve just told them that this is going to change their life. Better to just let them be positively surprised."
Beyond being a good gift-giver, Rutledge's findings may also have important implications for the study of depression. For instance, it's already known that people with clinical depression don't get as much pleasure from things that people normally find pleasure from.
"There’s something different about how they respond to rewards or how they make decisions," said Rutledge. "Maybe that has something to do with, in general, why they feel lower than most people."
Currently, Rutledge is applying his happiness equation to test people with depression and hopes to publish more research on the topic in the future. The current study was published online in the Proceedings of the National Academy of Sciences.
"Do people who are happy all the time also get more happiness from rewards, moment to moment, or is there something different about their expectations?" Rutledge said. "We don’t know yet. Those are the things we want to address."
CORRECTION: A previous version of this story misstated the total amount of happiness ratings Rutledge evaluated. We regret the error.