If you don't feel free, chances are you don't feel happy either.

Both of these words, free and happy, are pretty loose in their official definitions. Scientific studies have used various metrics to measure happiness; self-reporting, brain waves, psychological evaluations, and family member surveys. As for freedom, the studies mainly use the self-reported metric, how free a person feels.

When people feel less restrained by outside forces, when people feel that their life is their own to do as they please, they are happier.

Even when holding income, sex, education, race, religion, politics, and family status constant, we find that people who felt free were about 18 percentage points more likely than others to say that they were very happy.

Even people who think that the government should be less involved in daily life are happier than people who think society needs more rules. And it might be tempting to chalk this up to people who are poor feeling unhappy, regardless of freedom. It makes sense to think they would want the government to intervene in order to make them more wealthy, and thus happier.

But when you look at countries overall, you still find that freer countries are happier countries.

…in 1990, at the end of the Communist era, one cross-country survey found that 41 percent of Americans said that they were very happy—contrasted with just 14 percent of East Germans, 6 percent of Russians and Czechs, and 2 percent of Latvians. Of course, regimes behind the Iron Curtain were not just economically unfree; they were politically unfree as well.

Of course, this could also just point to the fact that the freer the country, the more prosperous the people. So you could say that being prosperous makes you happy. Except this would prove that free economies deliver more prosperity. So no matter how you slice it, more freedom means more happiness–even if prosperity is a necessary step in between.

But another study found that even prosperity might not matter as much as freedom when it comes to happiness.

Swiss economists Bruno Frey and Alois Stutzer made this point convincingly in the 1990s, comparing happiness levels across various Swiss cantons, which vary dramatically in how much political participation they afford their citizens. Cantons that allowed citizens more direct democratic rights, as well as meetings with leaders to discuss political and financial matters, proved significantly happier than cantons where political access was more restricted.