A burgeoning army of happiness researchers has discovered a strong correlation between age and life satisfaction.'
People in their late teens and early 20s report a high degree of happiness, on average, but the level falls away among the middle-aged. The nadir comes when people are in their early 50s. Happiness levels then tend to rebound in older age.
A new study by economists David Blanchflower and Andrew Oswald has bolstered the case for this "U-shape" pattern of wellbeing though the life course. They analysed seven massive life satisfaction surveys covering 51 countries, including Australia, and involving 1.3 million people.
The huge data crunch showed that U-shaped happiness curve – where well-being is high in youth, troughs in midlife, and rises again in old age – was strikingly consistent across a variety of different large-scale data sources.
"There much evidence," Blanchflower and Oswald conclude, "that humans experience a midlife psychological low."
They point out this midlife slump in satisfaction is "equivalent in magnitude to the influence of a major life event like unemployment or marital separation".
While there's some evidence to show women have slightly higher life satisfaction than men over the life course, gender differences are very small.
The pattern is also remarkably consistent across different cultures. A separate international study published in 2016 by researchers Carol Graham and Julia Ruiz Pozuelo found the "U-shape relationship between age and happiness" held up in 44 of the 46 countries they examined.
There is one interesting Australian caveat. An important study published late last year by Melbourne University economists Mark Wooden and Ning Li suggests elderly Australians might not conform to the international norm. Wooden and Li's analysis of life-evaluation questions asked as part of the long-running Household, Income and Labour Dynamics in Australia (HILDA) survey found that "life satisfaction falls quite sharply" as people enter old age (especially past the age of about 70).
So why is it that people start their adult lives pretty cheerful, one average, only to get the grumps in middle age?
According to Blanchflower and Oswald, researchers don't really know.
"The scientific explanation for the approximate U-shape currently remains unknown," they say in their paper "Do Humans Suffer a Psychological Low in Midlife? Two Approaches (With and Without Controls) in Seven Data Sets" published by the National Bureau of Economics Research.
One possible contributor to the midlife low is that those in their 40s and 50s are at a difficult stage of life. Many in that age cohort are juggle demanding careers with wrangling adolescent children and possibly caring for aged parents. But is that life stage really so much worse than others?
Another popular, if depressing, hypothesis is that thwarted aspirations and chronic disappointment contribute the middle-aged gloom. Although Professor Oswald warns there's growing scepticism about that theory.
Researchers are now wondering if the midlife low is somehow natural.
There's evidence that even great apes are prone to mid-life crises. A study published in 2012 found a "U-shape" similar to humans in the wellbeing patterns shown by a large sample of chimpanzees and orang-utans observed in zoos in Japan, the US, Canada, Australia and Singapore.