A few weeks after leaving the presidency, Thomas Jefferson wrote in a message to the citizens of Maryland that, “The care of human life and happiness and not their destruction is the first and only legitimate object of good government.”

For many conservatives and libertarians, the best way for government to make us happy is to stay out of our lives as much as possible. But since many Americans believe that government does have a role increasing flourishing, we should ask how it could use its influence more effectively.

A group of researchers set out to find a solution by asking, “If we wanted to have one less person in misery, what is the cost of achieving this by different means?”

“Happiness is caused by many factors, such as e, employment, health and family life,” say the researchers, “and we need to ask, How much does a difference in each of these factors change the happiness of the person affected?”

The team analyzed surveys of adults in the U.S. Australia, Britain, and Indonesia to determine which factors matter most for lifting people out of misery. What they found was that in every country, e was more important for happiness than education, though household e per head explained less than 2 percent of the variance of happiness in any country. Having a job, good physical health, and a partner (whether married or living as married) also mattered. But the most important factor in all three Western societies was diagnosed mental illness.

So how much could we reduce the prevalence of misery in the USA if we could miraculously abolish depression and anxiety disorders without changing anything else? Well, around 22% of the population have this diagnosis. If they were all cured, we could reduce the percentage of the population in misery by 0.107 times 22%. This is 2.35% of the whole population. That is large portion of the total 5.6% who are in misery.

By contrast, eliminating poverty in the USA reduces misery by 1.7% points, unemployment by 0.3% and physical illness by 0.5% out of the total 5.6% in misery. Taken together, those three factors barely make as much difference as mental illness on its own.

The report calculates that, in the UK, thecost to lift one person out of misery by reducing poverty would exceed$224,000 a year while the cost of treating anxiety or depression would only require around $12,000.

Obviously, we shouldn’t conclude from these findings that poverty, physical health, and unemployment can be ignored. These factors are often intertwined in a way that leads to significant levels of individual unhappiness and societal unrest. But the report does show that if we want the government to help reduce human misery we should give more attention (and possibly money) to finding ways to reduce the effects of mental illness.