It’s easy to look at the past with rose-colored glasses, but were we really all once much happier? A team of psychologists has constructed a novel method to measure historic happiness, and their results combine both expected and surprising results for four nations.

The idea that governments' role is to promote “Gross National Happiness” rather than Gross Domestic Product has gathered steam in recent years, becoming the official policy of Bhutan. However, success requires methods to measure how happy people are. Population happiness surveys have only been done systematically in the last decade, and scrappily in places since the 1970s.

Professor Thomas Hills proposed historic publications might give us a longer perspective. He compared the frequency with which positive and negative words are used in the 8 million books available online through Google Books, theorizing readers seek writing that reflects their mood, and editors give them what they want.

To test the validity of his method, Hills compared the recent years' publications with existing happiness measurements over that time. The correlation is far from perfect, he reports in Nature Human Development, but is good enough to use.

Hills then analyzed items published between 1820 and 2009 in the US, UK, Italy, and Germany and charted the approximate happiness of each over that time, providing an indication of the forces that affect national happiness.

The researchers found spikes in national happiness were sometimes generated by increases in national income but generally, it took a very large rise to have any noticeable effect in the US and UK.

Unsurprisingly, all four nations experienced sharp dips in positivity during the First World War. For the English-speaking countries, the sequel was even worse, but its effects are less clear on the Axis side, perhaps because Hills' measure does not allow for totalitarian censorship. The Civil War was also quite a downer for America.

Yet by Hills’ measure, Britain was even less happy in the late 1970s – particularly during the aptly-named "Winter of Discontent" and early Thatcher years – than during the Blitz. Hills notes America's lowest moment coincided with the fall of Saigon in 1975, as the Vietnam War came to a close, but the after-effects of Watergate (1972) could also take the blame.

If Hills’ work is to be believed, Italy was happier around 1830 and 2000 than any time in between, although it has averaged well been above the other three nations.

We may not know when America was at its greatest, and thus shall return to form, but its happiest 20th-century moment was just before the Wall Street Crash (1929).

Although increasing wealth does correlate with greater national happiness, the effect is small, suggesting governments might do better to make other things their priority. Longer life expectancy is another happiness booster.

"What's remarkable is that national subjective well-being is incredibly resilient to wars,” Hills said in a statement. "Even temporary economic booms and busts have little long-term effect. We can see the American Civil War in our data, the revolutions of 1848 across Europe, the roaring '20s and the Great Depression. But people quickly returned to their previous levels of subjective well-being after these events were over.

"Our national happiness is like an adjustable spanner that we open and close to calibrate our experiences against our recent past, with little lasting memory for the triumphs and tragedies of our age."