Is the midlife crisis real? Economists and psychologists disagree.

Two economists recently presented a working paper offering statistical proof for the existence of the midlife crisis. In a survey of 1.3 million people across 51 countries, the researchers found that people report a measurable decline in happiness, starting in their 30s and continuing until around 50, when they started to feel satisfied with their lives again.

"We're seeing this U-shape, this psychological dip, over and over again. There is definitely a midlife low," said Andrew Oswald, an economist at the University of Warwick and co-author of the study.

But many psychologists say the midlife crisis doesn't exist. "I've been doing research for pretty much my whole career on adult development, and I've never found age linked definitively to anything psychological about a person," said Susan Krauss Whitbourne, a professor of psychology and brain science at the University of Massachusetts-Amherst. "You can call it a midlife crisis. A quarter-life crisis. But whatever's going on with you personally, you can't blame it on age."

And back and forth the argument goes: "I don't know why some psychologists say it doesn't exist," said Oswald's co-author, David Blanchflower, an economics professor at Dartmouth College. "It's blindingly obvious. All we did was plot the data points."

"I don't understand why they're so set on this," Whitborne said. "They're economists. What if I tried to use psychoanalytical measures to index the economy?"

The idea of a midlife crisis originated in the early 1960s with Canadian psychologist Elliott Jaques. He was studying the creative habits of 310 famous artists such as Mozart, Raphael and Gauguin when he noticed a common trait: When they entered their mid-30s, their creative output waned. Some became depressed. A few died by suicide.

He then observed the same pattern among his clients. As people approached middle age, many of them became acutely aware their lives were finite and reported an increasing fear they might not achieve their goals.

Jaques's resulting paper, "Death and the Midlife Crisis," published in the International Journal of Psychology in 1965, gave rise to a new pop-science term and provided men with an excuse to get hair plugs or buy a sports car.

But in more recent research, several psychological studies have failed to find middle-aged anxiety or have disproved it altogether. The National Institute of Aging finds that only a third of Americans over 50 claim to have experienced a midlife crisis. Half attribute their crises to "inner turmoil and angst associated with getting older," while others point to a traumatic event such as a divorce.

Whitbourne has spent the bulk of her career tracking a few hundred people from their college graduations in 1965 to now, adding younger cohorts along the way.

"People do go through periods of self-evaluation, but it's not tied to age," she said.

"If someone close to you dies and you start to think about how life is limited, is that a midlife crisis? Or is it just a healthy reevaluation of your priorities?"

Oswald and Blanchflower have been studying happiness as it relates to age for more than a decade; their first paper published on the topic in 2004 put the nadir at age 37 for men and 41 for women. "No explanation is available even in the psychology literature," they noted at the time. A 2008 paper repeated the findings in developed and developing countries and again said that "what causes this apparently U-shaped curve is unknown."

Ultimately, they might both be right. Oswald and Blanchflower's dip might not indicate the existential angst Jaques theorized in the 1960s. It may instead be a general side effect of contemporary adulthood. The dip occurs during the time period when most people marry, form families, get mortgages and possibly experience unplanned shocks such as divorce or unemployment.

If anything, the dip recorded by Oswald and Blanchflower may simply be the statistical proof of what millennials are only starting to learn: "Adulting" is hard.