Companies in many sectors have been increasingly investing in the happiness of their employees. Companies like Etsy go as far as to create a Gross Happiness Index, and Google gather metrics to optimize the length of its free lunch lines - too long, and people are annoyed; too short, they don’t get to chit-chat.

As any investor should be able to measure its returns, a group of U.K. researchers say they've provided the first scientifically-controlled evidence of the link between human happiness and productivity: The study found that happier people are about 12% more productive.

The results, to be published in the Journal of Labor Economics, are based on four experiments that used a variety of tactics on a total of 713 subjects at an elite British university.

In three experiments, the University of Warwick team conducted happiness interventions on some subjects, like showing them a comedy film or giving them chocolate, food, and drink. The people who got this treatment were more efficient at a task later given to them than those who weren't. In the fourth experiment, the researchers measured productivity first and then questioned the participants about real-life shocks in their life, such as death or illness. The people who recently experienced pain were also less productive.

However, it cost the researchers money to buy the food and drink, and time to show the subjects comedy films. So it's unclear, in this study or real-life work setting, how many resources a company should devote to increasing happiness - in the hopes of a bottom-line benefit.

For workers, it may seem like a positive trend when employers care more about happiness and wellness. The authors of the study also suggest that their work could affect hirings and promotions. “If happiness in a workplace carries with it a return in productivity, the paper’s findings may have consequences for firms’ promotion policies and may be relevant for managers and human resources specialists,” they write.

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