How does the world feel? Ask Twitter
A Footsie-style "happiness index" that measures the mood of the world on any given day can now be accessed online.
Click on www.hedonometer. org and you can see a wavy line plotted on a graph that rises and falls, in much the same way as the FTSE 100 index.
But the peaks and troughs have nothing to do with the financial health of major companies. Instead, they represent the averaged-out emotional state of tens of millions of people.
A team of US scientists constructed the hedonometer from data obtained from the social messaging site Twitter.
Some 50 million tweets from around the world are collected each day and analysed for "happy", "sad" and "neutral" word content.
Words are assigned scores with the happiest and most positive placed at the top of a 1-9 scale. From this, an average happiness rating is calculated.
"Reporters, policymakers, academics – anyone – can come to the site and see population-level responses to major events," said Dr Chris Danforth, from the University of Vermont, one of two US mathematicians who developed the hedonometer.
The global website only went public today.
A dramatic hedonometer dip can be seen on Monday, April 15, the day of the Boston marathon bombings – showing how shock waves from such events resonate around the world.
"Our instrument reflects a kind of quantitative macro-story, one that journalists can use to bring big data into an article attempting to characterise the public response to the incident."
The hedonometer is based on a psychological assessment of around 10,000 words. Paid volunteers rated the words for their "emotional temperature", ranking the happiest at the top of the scale and the saddest at the bottom.
Averaging the volunteers' responses, the scientists assigned an overall score to each word. The word "happy" itself scored 8.30, "hahaha" 7.94, "cherry" 7.04 and the more neutral "pancake" 6.96.
At the bottom of the scale, the word "crash" scored 2.60, "war" 1.80 and "jail" 1.76.
Currently the hedonometer is updated every 24 hours, but further development could see billions of words collected daily to provide a minute-by-minute barometer of global happiness.
The scientists acknowledge that happiness is a slippery word that means different things to different people.