Economists at the University of Warwick, carried out a number of experiments to test the idea that happy employees work harder.
In the laboratory, they found happiness made people around 12 per cent more productive.
Professor Andrew Oswald, Dr Eugenio Proto and Dr Daniel Sgroi from the Department of Economics at the University of Warwick led the research.
This is the first causal evidence using randomised trials and piece-rate working.
The study, to be published in the Journal of Labor Economics, included four different experiments with more than 700 participants.
During the experiments, a number of the participants were either shown a comedy movie clip or treated to free chocolate, drinks and fruit.
Others were questioned about recent family tragedies,
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