What's true for Bart is true for most of us under the age of 50 or so, according to a new analysis of life satisfaction encompassing seven surveys and 1.3 million randomly sampled people from 51 countries.

Happiness, those surveys show, follows a generalised U-shape over the course of a life: people report high degrees of happiness in their late teens and early 20s.

But as the years roll by, people become more and more miserable, hitting a nadir in life satisfaction sometime around the early 50s.

Happiness rebounds from there into old age.

If you plot the age-happiness curves from all seven surveys on the same chart, the shapes of the curves rather than any absolute value are what is believed to be important.

The surveys asked about happiness in different ways – some framed it in terms of “satisfaction”, while others asked people to rate where they fell between “happy” and “unhappy”. So the absolute values of each line aren't directly comparable.

Two things stand out: first, the curves all follow the same general U-shaped trajectory.

Youth and old age are periods of relative happiness, middle age is something of a rock bottom.

Second, they generally agree the bottom of that U hits some time in the early 50s.

“There is much evidence,” the paper's authors conclude, “that humans experience a midlife psychological ‘low’.”

The exact causes of that low aren't entirely clear.

One explanation is that in wealthy countries, middle age is a particularly stressful time. People in their late 40s and early 50s are often at the peak of their careers, and many are dealing with unruly adolescent children to boot. 

For the rest of us under the age of 50, it may simply be enough to know that even if we're having a particularly bad day, statistically speaking things are going to get a lot worse before they get better. Have a nice day.