A quote from Arthur Brooks in City Journal, "Free People are Happy People:"
Freedom and happiness are highly correlated, then; even more significant, several studies have shown that freedom causes happiness. In a famous 1976 experiment, psychologists in Connecticut gave residents on one floor of a nursing home the freedom to decide which night of the week would be “movie night,” as well as the freedom to choose and care for the plants on their floor. On another floor of the same nursing home, residents did not receive these choices and responsibilities. The first group of residents—no healthier or happier than the second when the experiment began—quickly showed greater alertness, more activity, and better mood. A year and a half later, they were still doing better, and even dying at half the rate of the residents on the other floor.
This chart from the article:
Read the whole thing.