Do a country's inhabitants get happier as it gets richer?
Most governments seem to believe so, given their relentless focus on increasing GDP year by year.
Reliable, long-term evidence linking wealth and happiness is, however, lacking.
And measuring well-being is itself fraught with problems,
since it often relies on surveys that ask participants to assess their own levels of happiness subjectively.
Daniel Sgroi of the University of Warwick and Eugenio Proto of the University of Glasgow,
both in Britain, think, nevertheless, that they have an answer.
By examining millions of books and newspaper articles published since 1820 in four countries (America, Britain, Germany and Italy),
they have developed what they hope is an objective measure of each place's historical happiness.
And their answer is that wealth does bring happiness, but some other things bring more of it.
Previous research has shown that people's underlying levels of happiness are reflected in what they say or write.
Dr Sgroi and Dr Proto therefore consulted newspaper archives and Google Books,
a collection of more than 8m titles that constitute around 6% of all books physically published.
They searched these texts for words that had been assigned a psychological "valence"—
a value representing how emotionally positive or negative a word is—
while controlling for the changing meanings of words such as "gay" and "awful"
(which once most commonly meant "to inspire awe").
The result is the National Valence Index, published this week in Nature Human Behaviour.
該研究的結果就是本周發表在《Nature Human Behaviour》雜志上的《National Valence Index》。
Placed alongside the timeline of history, the valence indices for the places under study
show how changes in national happiness reflect important events.
In Britain, for example, happiness fell sharply during the two world wars.
It began to rise again after 1945, peaked in 1950, and then fell gradually,
including through the so-called Swinging Sixties, until it reached a nadir around 1980.
America's national happiness, too, fell during the world wars.
It also fell in the 1860s, during and after the country's civil war.