Since the 1960s, psychologists and economists have tried to study happiness with surveys and data. Their work cannot settle which theory is right, but it shows what tends to go with feeling good and judging life well.

Measuring happiness

Researchers usually separate two things. Experienced well-being is how people feel moment to moment; life evaluation is how they judge their life as a whole. A common life evaluation question, the Cantril ladder, asks people to imagine a ladder with steps from 0 to 10 and say where they stand. To capture experience, researchers use experience sampling, in which people are pinged at random moments and asked what they are doing and how they feel, or the day reconstruction method, developed by Daniel Kahneman and colleagues in 2004, in which people replay the previous day episode by episode.

These methods have produced some striking findings. In a 2010 study using phone sampling, Matthew Killingsworth and Daniel Gilbert found that people's minds wandered from what they were doing nearly half the time, and that people were less happy when their minds wandered, even to pleasant topics. Other studies found commuting among the least enjoyed parts of the day and time with friends among the most.

Self-reports have obvious limits. Answers shift with question order and passing mood. Still, scores agree fairly well with ratings by friends.

Money

Does money buy happiness? Within a country at a given time, richer people report higher life evaluations on average. But in 1974 the economist Richard Easterlin pointed out that in the United States, average income had risen greatly since the 1940s while average reported happiness had not. The Easterlin paradox is the finding that rising national income over time did not seem to raise average happiness. One explanation is that people compare themselves with others. Later researchers, including Betsey Stevenson and Justin Wolfers in 2008, argued that with more data, richer and faster growing countries do show higher life evaluations. The debate continues.

The relationship looks roughly logarithmic: each doubling of income is linked to about the same rise in life evaluation, whether one starts poor or rich, so a given sum means far more to the poor. In 2010 Kahneman and Angus Deaton reported that day-to-day emotional well-being in the United States rose with income only up to about 75,000 dollars a year, while life evaluation kept rising. In 2021 Killingsworth found no such plateau. The two sides then worked together, and in a 2023 paper with Barbara Mellers they concluded that the plateau appears only among the least happy people. For most people, feelings keep improving with income; for the unhappiest fifth or so, more money stops helping beyond a point.

Adaptation

People adjust to change. A 1978 study by Philip Brickman and colleagues found that recent lottery winners were not much happier than a comparison group, and that people paralyzed in accidents were less happy but not as unhappy as one might expect. Researchers use the phrase hedonic treadmill for the way people adapt to gains and drift back toward a baseline. That study was small, and later work following large samples for years has shown that adaptation is often incomplete. People adapt fully to some changes, such as marriage, and only partly to others, such as serious disability or the death of a spouse.

A related finding concerns prediction. People routinely overestimate how strongly and how long a future event will affect them. A cousin of that error, the focusing illusion, is that whatever we are thinking about seems more important to happiness than it really is. Asked about life in California, students in the Midwest expected Californians to be happier, thinking of the weather; in fact the two groups reported similar life satisfaction.

Genes, people and limits

Twin studies suggest that genes account for roughly a third to a half of the variation in well-being between people. That does not mean happiness is fixed. A popular claim that 40 percent of happiness is under deliberate control rests on a misreading of the statistics. The most reliable correlates of happiness are strong social relationships, good health, secure work, trust in others and a sense of freedom to make life choices. A 2002 study of very happy college students by Ed Diener and Martin Seligman found that all of them had strong social ties.

Caution is wise. Many results are correlations, and causation can run both ways: happy people may find it easier to make friends. And the research measures what people report, which, as earlier levels showed, may not be all that well-being is.

Worked example: the raise and the commute

Kofi can take a job paying 20 percent more that adds an hour of commuting each way. A 20 percent raise is a modest step on a logarithmic curve, and he will likely adapt to the higher pay quickly. Commuting, by contrast, is among the least enjoyed daily activities, and it would come out of time now spent with family and friends, some of the strongest correlates of well-being. The focusing illusion warns that while he is thinking about the salary, it will loom larger than it should. If the money would relieve real hardship, the balance shifts, since that is where income matters most.